Is this a good selection of parts for a gaming computer

All you really need to play most hardcore and high-end games is a lot of memory, a fast processor, a fast graphics card with lots of memory and lots of hard drive space. Some thermal cooling is also a good idea.

Memory - about 2 - 4 gigs should be a good start, 8 if you can afford it.
Graphics - 256 MB is a start, but I would go 1 gig or more. ATI is a good brand for gaming and NVIDIA is popular too.
CPU - Any AMD with 3 gig or more, dual or quad core (there is also a 6 core processor available) ir an Intel 4 gig and up (ie, I7 Quad).
HD Space - Get at least 1 terabyte for your application and game installations alone and place a second drive for your operating system and page file to have optimal efficiency for your game frame rate.
Cooling - Have a few chassis fans if you experience heating and crashes caused by overheating and make sure the CPU and graphics card are cooled with their own fans. Keep your PC well ventilated. I know this doesn't seem important, but you would be surprised what kind of performance loss you get because of a hot box.

Final tips... use corded peripherals for controllers and not wireless infrared or laser devices, they often don't refresh as fast as a corded device and tend to take up slightly more computer resources. Close all background programs and unneeded startup programs, defragment on a regular basis and don't always opt for the game's best quality as some game developers like to make the eye-candy a little too sugary for even the most high-end computers, especially if the code created to make such high quality settings are written very badly. Some old games can slow down a new computer based on bad scripting.

I hope this helps as I have been updating my PC often for over 20 years and it will never stop getting more high tech. It's getting to the stage where I can barely keep up any more and eventually I may have to give up and spend the rest of my life fishing or something...