Ok well i'll give you a quick description of what would be a pretty good system:
AMD 64 3200 + (Good solid proccessor you can't go wrong)
1GB RAM, 2x 512mb sticks, have a look round make sure its compatible with your motherboard, Corsair or kingston are good makes
Geforce 6600GT, Another good card, Nice price, Try and go for the 256mb version
Harddrive, make sure its 7200RPM, thats a nice average speed, the size is up to you
For your powersupply i reccomend a 500w supply, but DO NOT pay under $50-60 or it will be... rubbish.
Have a look on www.newegg.com
for all this stuff, i'd get you links but i'm kinda busy right now, i hope this helps.