fps problems cs 1.6

Hi, im having problems with my cs 1.6, I sometimes get a minute of smooth 100 fps before it drops down to 30 for the rest of the game, sometimes I dont. It chugs more so the more players that are on the screen. I used to get 100 fps solid through 6 smokes
im running nvidia 6600 gt, 3.0 processor (dual core) gig of ram, ect..
I have tried many things
firstly I heard newer drivers didnt work as well with games like half-life so I tried older ones, 66 series was apparently good for it but it only made things worse. I tried about 20 diffferent sets of drivers but nothing helped. I also booted in safe mode and ran a driver cleaner at one point, along with anti virus and spyware killers. But it didnt make a difference I had just reformatted anyway. I followed the dual core thread on major geeks and tried fix 2, since that is the one that applies to my game, but when that didnt work I tried the rest anyway :S
im currently using ztweaked drivers (guru3d.com) they are gaming drivers for nvidia gt cards.
I dont have many processes running in the background. but it shouldnt matter anyway.
the drivers lock refresh rates, anti aliasing, v-sync ect. I also have my card set to high performance. I used to get high frame rates in hl2 let alone 1.6...
if I think of anything else to say I will but if anyone can fix this PLEASE HELP