I too had this problem on my Macbook Pro (exact same as yours). What I did was download the latest forceware drivers for the Nvidia Geforce 8600 GT. It said that it couldn't find any drivers. So, after some Google searching, I found a way to go into the .inf for the forceware setup and trick it into downloading the drivers. +This actually worked+. The drivers were recognized and installed. I really have to run, so I don't have the time to locate that forum post again, unfortunately.
However, I realized afterwards that I only had Bootcamp 1.3. If you have Bootcamp 1.4, according to the user on the forums, you do in fact have the latest Beta forceware drivers installed (i.e. the exact ones I had just forced the setup to install). Sure enough, I got the same performance after reinstalling the latest Bootcamp drivers from 1.4.
I'm sorry if you already had Bootcamp 1.4, and this was no help at all. I just figured I would give all the info I could on the subject.
Sorry you're having issues, hope they get resolved 🙂.
Message was edited by: modernlovers