Well a 8600 has similar performance to the 7800, as does the 8800 has similar performance to the 9600, It's the same for almost all nvidia cards, where *600 has the same performance as the (*-1)800. Understand? Or in words, the high end card of generation 1 has the same performance as the mid range level card of generation 2.
Anyways, back on topic, yes, you should be able to play the game, it just wont look all that shiny.
I've had an 8600GTS before and it was quite a good card.