Where can you download Pixel Shader 1.1 or higher

Pixel shader 1.1 (and later variants) are hard-coded into the video card and its drivers. If you have a fast processor and a good amount of ram, you may be able to get around the pixel shader requirement by downloading "3DAnalyze" and "Swiftshader 2.0" to emulate pixel shader.

More likely, the best option is for you to simply replace your video card with one which has native support for pixel shader.

The above answer is dead on target! Let me add to this fire.......
Although there are work-arounds to the pixel shader, it is ill-advised to download a patch or third party software to achieve what comes nativley in the newer video cards. The competition is so tough in the industry, what would have been a top of the line video card last month, is now the cheapest card on the shelf!
Remember that even if you do get a third party software to achieve what it is that you want in a display, the OS and computer will have to work harder to maintain the demands of not only the third party software, but any additional workload that the software generates. Memory allocation is reduced because the demand of the third party software is memory intensive. Thus, reduced performance. Emulators do not work with every game, applications or systems. Not to mention, calling on the drivers to perform out of their scope, can also lead to corrupt system files and fragmentation of the system partition. Emulators temporarily "change" critical system and driver files per demand, to allow the system to adapt to the new drivers and dll files offered by the emulator. After the emulator is no longer needed, some times, the files don't get "put back" or restored to the defaults, and you have a mess on your hands! Listen to the answerer above, and get a new card!
You need to get a better graphics card. However there is a way around it.

There is a website (see Related Links) that has a tutorial for getting over the problem.
Pixel Shader is a hardware capability. However there are Pixel Shader emulators available which mimic this capability for compatibility with other/older chipsets. One of the most effective of these "emulators" is "Swiftshader" from a company called Transgaming. (See Related Links)

It is more advisable to try to use a Video Card which directly supports the capabilities your game or application is designed for, however, Swiftshader is not bad if you want to try to get your app running to at least gauge whether a new video card investment is worth it or not. Swiftshader is not free, but a demo is available to take for a spin.

The following cards support Shader Model 1.x:
- ATI Radeon 85xx Series (1.4)
- ATI Radeon 9000 Series (1.4)
- ATI Radeon 9100 Series (1.4)
- ATI Radeon 92xx Series (1.4)
- NVIDIA GeForce3 Ti (1.1)
- NVIDIA GeForce4 Ti (1.3)
The following cards support Shader Model 2.0:
- ATI Radeon 95xx Series
- ATI Radeon 96xx Series
- ATI Radeon 9700 Series
- ATI Radeon 9800 Series
- ATI Radeon X7xx Series (2.0b)
- ATI Radeon X8xx Series (2.0b)
- NVIDIA GeForceFX Series (2.0a)
The following cards support Shader Model 3.0:
- ATI Radeon X1x00 Series
- NVIDIA GeForce 6 Series
- NVIDIA GeForce 7 Series
Some laptop have in board cards that do as well. My ATI Express 200M supports Shader Model (2.0).