I would strongly recommend NOT to attempt to run a GTS with that board. The PCIe slot often runs at 8x speeds and will the card will be gasping for bandwidth and you will get graphical corruption and freezes. Also the Chipset isnt strictly 100% compatible with PCIe standards, its just an add on by the MB manufacturers as far as im aware. i'd get a cheap Intel 965 if your on a tight budget.
I tried a 7950GX2 in a machine with the same chipset and had massive issues. The 8600GT is a VERY poor card and low bandwidth, the 8800GTS is FAR more powerful and spending £150 on a gfx card on a system with a £30 MB is asking for trouble.
Just to recap, i'm 99% certain that this combination of card/motherboard will give you no end of trouble.