so for that,you can get basically quite a decent rig:
cpu:athlon ii x4 640-$90
mobo:asrock 890gc extreme3-$120
ram:any 4gig decent ddr3 from a good manufacturer-40$
psu:what mouse24 suggested,that is decent even for cfx
case:nzxt gamma-30$(very good case,dont get carried away wid the price)
gfx card:what mouse24 suggested,is fine-160$
hdd:wd caviar green 500gb sata-30$
totals up to 535$,now get a decent gaming kb and mouse or oem win7 for 70$..
you can get the other one not selected any time after you have some cash.
totals up to 605$ so ur not going over the top as in case of mouse24 rig and getting a very good mid-high end mobo
I am not saying mouse' rig is not good but with this one,u got it cheaper.
HOPE IT HELPS