counter-strike win 2000 problems!?!

ive been playing CS fine for months now.... but after i formatted my hard drive and upgraded from win98SE upto win2000 i start to play CS, and in both lan and online games the mouse movement is very jerky...

I'm running it at 800 by 600 (i tried running in 640 by 480 but its so damn low res lol) in direct 3d mode with an ATI Rage 128 card (32Mb, expert 200 driver). i found out that using direct 3d mode lessens this jerkiness a little (rather than using open gl mode) but still not enough! :S

this is really frustrating! is it something to do with win2k? ive updated my drivers for my graphics card, and fiddled with the mouse settings in the game, but no luck!?!

btw i made sure that the settings i used in CS r the same as when i formatted