not sure you really need a 8600 gt if your comp was 250 bucks and your only gunna have 1.5 gig ram. depends on what your doing with it though. for gaming it will help, but if your editing or doing anything else, just upgrade a ton of ram
if your computer was as cheap as you said, before you get a new card make sure your motherboard supports it. and i'm not sure how ell a good video card will jive with crap components.
just put money where you think you will use it the most.