Actually arma2 requires a pretty good graphics card. Here is a quote from a magazine reviewing Arma2 - "And a really good rig - even our beefy 4870x2 powered rigs struggled with this at reasonable settings" I'm pretty sure that it's requirements are an 8800gt minimum, and this is at lowest possible settings. I would recommend at least a 9800gt/4770 if you're planning to get Arma 2.
Well I plan on overclocking the processor also hopefully to at least a 2.5ghz or more. My video card is a ASUS GeForce 9500 GT 1GB 128-bit DDR2 PCI Express 2.0 x16 HDCP Ready SLI Support.