Cod4 multiplayer lag

There is a chance that Windows' security programs or third-party software is conflicting with the game. Try running it with Windows Firewall disabled and your virus scanner either set to [Off] or with CoD 4 on the exception list.

You say that you cannot run the game in multiplayer mode, but how does single player work?

-K

Either the servers you join are hacked or poorly hosted, or you have a firewall/AV or malware software working in the background, flooding the ports your using.

Also, you might consider running a speedtest on www.speedtest.net to check your ISP parameters.

Cheers