EggXpert

I just bought it today, the Singleplayer works fine but, when I go to run the multiplayer it says iw3mp.exe stopped working

and closes out of it saying "we'll notify you when it begins to work"

I'm using vista os, help would be greatly appreciated

Oh yeah I downloaded the new patch so I don't think that's the reason. 

http://cod4boards.com/viewtopic.php?f=4&t=246

Many people are having an issue when launching the multiplayer portion of Call of Duty 4.

Tips:
Reinstall the game
Update your Drivers

There are some issues running CoD 4 Multiplayer on some onboard sound cards. Users with RealTek(TM) onboard sound cards and Windows(R) Vista will need to use Microsoft Audio Drivers 6.0, which can be found at http://www.microsoft.com. Users with Sigmatel® onboard sound cards need to install all Windows® Vista updates, and the latest Sigmatel drivers from http://www.dell.com.

If you are running the game from a secondary partition, download the latest BIOS updates from your motherboard manufacturer in addition to following the above instructions.

A fix will be posted here once Activision/Infinity Ward releases more info on this error

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