a Gddr3 256mb is better than a 512mb gddr2, so see if you can get more information about that card's specs
if that card is a gddr3 512mb, you probably won't need it unless you play high resolutions, but the 8600gt stinks in most games at high resolutions anyways...
but I recommend you go PM AMD GT Player because hte 7950gt trounces the 8600gt, and you can get it for only $10 than the 8600GT