Easy to build, if you have already done it before. new to building (putting everything in) it can be alittle stressful but im sure you could do it, if not..google it? lol. $500 would build you a Good computer. nothing super uber leet but something to play most games on High or so. AMD is Cheap but intel is better imo. Geforce is better then ATI and most of the time cheaper if you ask me. what kind of computer are you looking to build? what games and what settings do you wanna build for?
This is my Spec. nothing Great but i can run most games on High. i think i put about $300-400 into it! already had the case and HD sitting around. CPU/motherboard/video card/ram and power supply all new.
Random case (not worth alot, modded with star wars stuff tho)
Mother board is M5a-78L-M LX plus
Geforce 650 TI
600W ATX ILG-500R2 power supply
8GB DDR3-1333 Ram
250GB HD (not SDD)