Good gaming computer

I can't help, but I want to know the same kinds of answers..... I'll bump the question up for ya.

With that budget, I'd probably go for an "AMD Athlon64 130nm 3500+ 2200MHz/2.2GHz 512kb Socket939". Then you need a suitable motherboard with the the right socket (i.e. Socket939 in this case). If you have an old graphics card (I assume it's AGP?) you have to make sure you get a motherboard that has AGP and not PCI-express. Lastly, you need RAM. If you want to use your old RAM, you need to make sure you get a motherboard which has support for the same type as your old computer, for example, DDR PC2700/3200 or whatever your RAM is. If you're planning on purchasing new RAM, I'd go for 1GB. 512MB will do in most situations, but if you want to run games like Half-life 2, Doom 3, or Battlefield 2 at high detail settings, you should have at least 1GB (this will of course require a pretty good graphics card).

So to sum things up, the important thing is that you get a motherboard (ATX) with the right socket for the CPU you're buying, and with support for the right type of RAM and right type of graphics cards (AGP or PCI-Express). Anything else is a matter of budget and preference.

Edit: The CPU I suggested probably costs almost $400 alone, so you might want to get a somewhat cheaper CPU. The principle is the same, though: Buy as fast a CPU as you can get while still having enough money for a sufficient motherboard (and possibly RAM).

if you can use the existing card ( what is it ) and the existing case ( what is it ) and the existing ram ( what is it ) and the existing power supply ( what is it ) 400 balloons ought to get ya something fairly decent. Are you certain all these components are fried ? did you stick your tongue on the mother board or something like that ? ( just kidding )

Asus and Asrock manufacture decent gaming boards, and on tight budgets socket A boards are nice although antique.
Have you the time and desire to slap a system together yourself ? It's a lot of fun and really not very complicated at all. Come back with some specs on what you already have, and what you want and I'll be more then happy to do some online shopping for ya and post a variety of components for you to look over within your price range.