HI, i think this problem may have been overlooked or put to bad computer componants, but i do believe that windows 7 has a few issues with call of duty 4.
windows 7 x64
nvidia geforce 295
intel i7 920
asus rampage 2 extreme
corsair xms3 - 1600 - 12gb
I never had this lag problem before while using older hardware. basically when i first load up the game, my fos stays at 250, but drops to 30 and comes back in a split second. it does this repeatedly for a bit, goes away and then comes back again later. if any of you know what game loss is, mine goes from 4 to 233 (or around that area) and goes back to 4.
i also play mw2, aion, guild wars, cod2, and red faction guerilla all in high graphics and this lag problem doesn't happen to any of these games. in fact i dont even play call of duty 4 in high graphics and still get lag
I've played COD4 a lot on Windows 7 64-bit, and have never experienced what you're describing, so I don't think it's a Windows issue.
I'm running it on a C2Q, 8GB DDR2, Asus P5Q-E and crossfired 4870's. I don't think the processor/RAM/MB would be causing this issue, so I'd be looking at your graphics drivers as the most likely suspect. Which version are you using, and have you tried updating/rolling back? Sorry I can't suggest ones to try, but the last Nvidia drivers I used were in XP on a 6600GT, so I'm not too current I'm afraid!
I also encountered this problem. I am playing CoD4 on a laptop, Core2Duo P8600, Mobility Radeon HD3650, and 4GB RAM.
I ran CoD4 with everything maxed out on Vista at around 50 frames. When I installed it on windows 7, I had a jerky, laggy motion, regardless of how much I lowered the settings. I have the latest drivers from ATI and the latest version of directx, so I have no idea what the problem is.