Very strange Call of Duty 4 lag problem...

Im getting some pretty strange lagging with Call of Duty 4: Modern Warfare. Now i know a good amount about computers and i've fixed lag problems before but i've never had something like this:

Symptoms:
When I click COD4 Multiplayer, it takes like a minute to load staying only on the splash screen

When I click to join a server it takes 10-15sec to start connecting

When I get into the game, it runs smooth for about 2-3 minutes then some major lag hits for like 15 seconds and then goes back to normal. Then it runs smooth for for 2 minutes and lags again for 15 sec and repeat

Same thing happens in single player (except game loads up right away)

What I tried:
Enabled ports, even set to DMZ, that changed nothing.
Reinstalling the game, nothing
Reformatting, nothing
Updating punkbuster with pbsetup, and nothing
I end tasked both punkbusters and tried playing single player and same thing
Played single player offline, still lag
Hooked up directly to modem, nothing
Turned all settings to lowest (including resolution), still same thing
Updated video card drivers (they always were)
Monitored CPU and GPU temps, and they were both fine

My specs easily cover the minimum requirements:
AMD X2 5000+
2gb Ram
Gefore 8600GT

Any suggestions on how to fix this? I have no idea what the problem relates too. Any ideas? The game ran fine about 4-5 months ago, but the problem started like 4 months ago.

At what resolutions and graphics detail setting do you play the game ?

Update your motherboards bios(flash) and try again, could also be faulty hardware, anyway this is weird...test your 'green' nVidia on someone elses PC - LOL

i HAD THE SAME PROBLEM TOO. I am just now considering (after a year of not being able to play IT) getting a new video card because my primary (regular) monitor burned out in the vid card. I am reading this forum to consider which vid card too get. AND I'd like some answers.

It looks like, Even Call of Duty5 modernWarfare2, Requires greater than ATI1600XT, or, Nvidia Geforce 6600GT.
So, I may check out CD4 again with an way better vid card than my x1050 ATI.
I allready made my RAM be at 2gb.
But, it still didn't work for long (Call o'Duty4).
And, I found many problems with Direct X 9 because !I want to run old games!.

So, I may get it too work by installing a way better VIDEO CARD. Damn!
But Rock On!!

i had this problem with my (am2) athlon x2 4000+ using an x1650 card and 1.5gb of 667ram, i fixed most of the slow down by overclocking my cpu, it seems to be somthing to do with amd x2's memory bus. it was like sudden stutters yet the frame rate was fine @42fps constant. very strange problem., never had it with my 3200+@x1900xt + 1gb-ddr400 (939)