From the CPU thred you had going I can tell you the you don't need to spend much at all on a video card. Anything that can handle HD decoding is fine, i.e. 8600 GT like I have or an equivilant ATi card.
ATI 1650 Pro (512Mb) would do you just fine (HIS with the Arctic cooling aftermarket cooler is sweet with an all solid state capacitor layout). Its like 30.00GBP and probably around 50.00USD (one of the cheapest PCIe cards available). Good one for my flatmate and he is real chuffed!! ATI=better image quality right?? 8600 GT is just not good for anything...
The ATI 1650 Pro actually quite good for the odd bit of gaming (it will render Doom 3 in Ultra detail at 1024x768 res.) It will also accelerate x264 playback, etc.