I recently posted a problem about my FPS drop for CS 1.6 using the 8600GT. I was surfing some of the other forums and found that the recent 8600GT Drivers are not OpenGL friendly. This could possibly be causing the out of control FPS that i am having in CS. Going from 100FPS to 15FPS to 60FPS to 15FPS to 100FPS and all over again...Also the card is known to cause a blue screen crash for some mobos and bios'. For all the people that are having problems with their 8600GT or GS cross your fingures that nVidia comes out with an update that fixes these problems that all of us are having in their next Driver release.
Another thought ------- I am thinking about keeping the 8600GT(since its been 30 days >:|) but getting a 7950GT 512onboard card to replace it. And give the 8600GT to my sister for her Sims2 games. Is this a good choice in cards at the 189.00 range that newegg has it at? PLEASE LEAVE FEEDBACK EVERYONE!
Pretty sure that CS 1.6 does not use OpenGL. Anyway, that sound like an awfully bad driver issue...uncommonly bad. Try reinstalling the driver using driver cleaner. Do you have problems in any other games?