Butt,
In additin to Squiddley's post, here's a few recommendations from myself you might want to consider.
Games require horsepower in large quantities. Go for big chip speeds, Intel if budget allows, or AMD if not. Loads of RAM 128MB minimum with Win 95/98/Me and 256MB minimum with Windows2k. I understand the Videologic Sonic Fury is a good sound card, and not expensive. Comes with onboard DSP's for surround and such I think. Graphics cards are important too. I run an nVidia TNT2Ultra. Go for an nVidia GeForce 2 Ultra, this baby will out power our six figure Silicon Graphics Onyx2 virtuality engine for about £300UKP...!
Hope this helps,
Aq