look at Newegg.com here is a list of supplys ur gonna need to buy if u wanna build it
new procceser if your going cheap go amd  speed probly around 2.0 - 4.0
ram about 2+ Gigs
hardrive go western digital if you down load stuff your gonna want around a 750+ gigbytes if you dont stick with a 250 - 320
motherboards wat your looking for is something taht has 2 - 8 sata slots 2 - 4 slots for ram make sure to match ram with your mother board if you need help let me no pick something that allows your moniter so if you have vga cord make sure your mother board supports it if you have a ps2 mouse and key board make sure your mother board supports it

buying a processer your mother boaard needs to be made for the proccesser you are buying this takes some looking in to if you need help let me no

if your getting a video card for  starcraft 2 make sure rto chcek specs with sc2 and match with the card you get
make sure u buy a new cause if your looking for a cool decked out gaming cause that is large thats support hella harddrives look in to the atec 5900 or 5000 if forget which
if you wanna get a new wireless card they have them but relize u wil spend at least 500 + if you dont buy things on sale luckyly this is the best itme of the year to buy this shit any ways if you need any more hep let me no