1) Download COD4. You can get this anywhere, just search the web, torrents will be better though. (I cant post outside torrent links)
2)Use the crack i posted below... (copy and replace the iw3mp.exe file to the directory.)
Virustotal. MD5: 9a90f6830c85202bcec844ee7da4dc74
3)Download qtracker Qtracker Downloads
4) Run qtracker, do a full server refresh for cod4 (you have to add the game to your list) and run the game through Qtracker.... tell me if this works!