Can you turn your computer into a wireless access point without a wireless router for your Nintendo ds

Yes. See below article from binarylotus:
Connecting your Nintendo DS Wi-Fi to a Generic Wi-Fi Adapter With the release of Mario Kart DS, Nintendo has entered the online gaming arena. Unfortunately, while the NDS does have (some) 802.11b support, it does not feature WPA support (only lower strength security WEP is supported). While Nintendo does offer a Wi-Fi USB adapter that can remedy this problem, you may be able to get by without it. This article might save you a cool $40.

Scenario: You have an existing wireless network, but you have to (or better yet, want to) use WPA, WPA2, or something other than WEP for your encryption standard. Or, you don't have an existing wireless network. Nintendo's official solution is to buy their USB Wi-Fi adapter, but this solution requires you to use Windows XP or Vista. Mac and other users are totally out of luck at this time. However, if you've already got a Wi-Fi adapter of some kind (or if you're like me, can find a generic adapter for cheap - some are out for as low as $10 after rebate nowadays), you may not need to buy the adapter. You'll need the following:

• A computer (safe to say you likely have one of these if you're reading this)
• A wireless network adapter that supports the 802.11b protocol (b+g is fine)
• A secondary network adapter that connects to your ISP (either directly, or through your network). This can be a wireless or a wired adapter.
• A broadband internet connection (required by Nintendo Wi-Fi)

For the purposes of this article, I'll be using the Hawking Technology HWU54G adapter (ver 2), but many other adapters should work. Be warned though, that not all adapters will support the methods listed here. Also, I'll be detailing the procedure on Windows XP, but the general procedure should work on other OS' as well. The important part is your adapter's value add software features. Step One: First we need to install the Wi-Fi adapter (if it isn't already). If you're using a PCI adapter, power off the machine, and install the card into your computer. If you're using a PCMCIA/PCCard (laptops) or USB adapter, install the drivers and software, then connect the adapter. In case of doubt, consult the manual. Optional pre-setup step: If you can, get a copy of NetStumbler and find out what wireless channels and SSIDs are in use in your area. Make note of them for later. Provided you have your adapter installed, NetStumbler should work fine. Close NetStumbler when you're done. Step Two: After you have everything installed and ready to be configured, load up the manufactuer supplied configuration utility for your Wi-Fi adapter. You may be prompted by Windows to let it handle the adapter; do NOT allow this! Use the provided utility that comes with your adapter. Currently, the Windows Wireless Zero Configuration utility (or in other words, the built-in Wi-Fi capabilities of Windows) doesn't work for what we want to do (or at least, I haven't been able to get it to work). Step Three: We need to make the adapter act like an access point that the NDS can connect to first of all. Look for an option to have the adapter set itself as an access point (or use ad hoc mode). The Hawking adapter uses the ZyDAS chipset and configuration utility and supports this functionality. Step Four: Now that your adapter is set in access point (or ad hoc) mode, it's time to configure the settings. For the ZyDAS config Here the "More Setting…" button has been selected and the next menu has popped up. We need to set the SSID (System Set ID) most importantly of all, and those of you with adapters that feature "turbo" modes (ie, those that advertise speeds of 108mbps) will need to turn that feature off. Select the "Change" button, and enter the SSID you want to use. If you used NetStumbler earlier to find out what SSIDs and channels are being used, change your WiFi channel to one that's not being used if possible; otherwise, select the one with the least amount of SSIDs. Also, do not use the same SSID as another that you've found. If you have a setting for power use, it's recommended you keep it at maximum for now. Step Five: The next step is to set up some security measures. The first of these is WEP encryption. Again, the DS does not support WPA, WPA2, or other methods; this is as good as it gets. In any case, either "Shared Key" (better) or "Open System" should work, so select one of those. WEP is the default here, but may not be for your adapter; select it (if you have the choice of key length, stick with 64 bits). Now comes the fun part. For the ZyDAS utility, select "Setting", then "Change" in the new window that appears. The trick here is that you need to make a key value (password) out of numbers (zero through nine), and the letters A through F, and the key value has to be 10 characters long. If you have an option to use hex or ASCII characters (as seen above), stick with hex. If you have four fields as shown here, enter the same key value for each (the NDS only uses the first key value anyway). If you have a selection as to what key value to use or default to, stick to #1. Step Six: We're getting there, don't worry. With WEP enabled, we have an access point of sorts that we could connect the DS to…but at this point, it's not connected to our internet connection. We need an option to connect the adapter to the other adapter in the system that is, and that's achieved by bridging (that is, making a connection between the adapters). With the ZyDAS driver, this is done by setting the "Bridge Adapter" box to the ethernet adapter present in my system. If your utility doesn't offer this functionality, you may still be able to have Windows bridge the adapters for you. Open up network properties, select the "access point" and your main connection, then select Advanced -> Bridge Connections. This will establish a link between the access point we've set up and your main internet/network connection. Note: in the interest of security, it's recommended that you disable the access point when it's not in use. Step Seven: Let's play! Fire up Mario Kart DS or other game that uses the NDS Wi-Fi feature. Enter settings, then search for an access point. You should see the SSID you gave to your access point in step four; select that. You will then be prompted for your WEP key; enter that. The program will then test the connection. If successful, you're ready to go! Step Eight: Optional, but recommended to shore up security. Your DS, like most other network adapters, has a unique (hopefully) identifying code, called a MAC address. As seen in the second screenshot, some utilities have a MAC address filter you can use to tell the adapter to only accept connections from certain MAC addresses. First, we need to get your NDS' MAC address. Go back into the Wi-Fi setup program. Select the option to view system settings. Record the MAC address. Now, set your access point to only accept connections from MAC addresses you enter, and type in the address to have it accepted by the access point. Step Nine: As step eight, optional, and can shore up security. SSIDs are normally broadcast to allow others to find them, but this can lead to people snooping on them. You can turn this option off in most utilities. Since you've already connected and saved the settings, this shouldn't present problems. All in all, the big problems you'll face are not necessarily that you can't do the steps required here, it's that the utility/value add software that comes with your adapter may not be up to snuff. There's no guarantee that this will work with every adapter either. Hopefully sometime there will be a way to configure this with only the native utilities and functionality in the OS, but at the present time, that doesn't seem likely to happen. In any case, good luck, and happy online gaming! Other Items of Note:

• The downloaded driver for the Hawking adapter has a broken version of their utility; use their CD install (if you must have the newer driver installed, uninstall everything, install the new driver, pull out the files from the InsTemp_USB dir, uninstall that driver, install the old one, then do a driver update from Device Manager. Manually point to where you stashed the new driver files, and point the wizard to that directory.
• The Hawking adapter gets quite warm during operation; you may want to try turning down the power setting. This may also be useful for notebook users needing to conserve power.
• Because the Nintendo Wi-Fi adapter is essentially a rebadged Buffalo WLI-U2-KG54-AI, I expect this product to work as well, but again, no guarantees. The advantage the Nintendo version has is specific software support.
• You may need to turn off the Windows firewall off on your adapter, if it is turned on (WinXP SP2 users should be especially mindful of this).
• When in ad hoc mode, your access point will only go up to 11mbps. You can have multiple DS' connected to your access point, but the limit will be around 5 or so units, as each DS takes around 2mb of bandwidth each (at least, reportedly this is the case; the Nintendo adapter accepts only five connections).
• You can use a 128 bit key instead of the 64 bit key used above - simply select 128 bit in the adapter utility, and enter a 26 character long key value instead of a 10 character long one. The DS supports up to a 152 bit key (or 32 characters), so a 256 bit key won't work.
• This document was partially inspired by a guide written by "Darkwind_776″ over on the Nintendo forums. His guide was written for the Gigabyte RT2500.
• Recently I purchased a CompUSA 54g Wireless LAN USB adapter model (SKU: 333626) which came out to $3 after rebates. It uses a very similar ZyDAS utility and can be configured the same way.