well, i can't really help that much but i was planning on getting a XFX Radeon 5770 i heard it was pretty decent and can run ArmA II pretty well (which is one of the main reasons i am getting it). Its Under $200.
Nvidia 9800GT would probably suffice, and probably quite cheap... Ok its not the latest gpu in the market, but im still running my 8800GTX on at least medium on arma2.. But the 8800gtx is a double slot jobby, but I think the 9800 is a low profile 1 slotter, unless that's not what you meant xD
i have hd 4600 it runs arma 2 with evrything on low-medium except resolution in pretty decent fps ( playable at least)
mw2 runs good on it aswell as other strategy game i play so its pretty much answering my needs so far
The key to modernising any weapon is covering them in glue and tossing them in a barrel of M1913 rails until they look "Modern" enough.
Many thanks to [R-DEV]Adriaan for the sig!