ive tried setting affinity to only 2 cores but still no joy
I must admit i thought CS (1.6) doesn't use more than a single core?
what's your netgraph saying? try using rivatuner or similar to force the fan speed to 100% and see how it performs then.
try running a dvd or bluray while you have the game open...
Disable onbaord video (if you have it) and just double check your nvidia control panel to see if you've got your 550 selected for cs and other games... on my laptop i'm running onboard graphics for flash, web browsers, desktop etc and the standalone graphics for games.
check your bios settings for ram and cpu, check they're actually running at the correct speeds/timings
grab a copy of hirens boot cd and do a memtest + disk analysis? :)