Overview
Look inside to find out how to do this simple trick.HINT: SP = MP
MAIN
Backup both iw3sp.exe and iw3mp.exe and put in a archive [7z | rar | zip]
now delete iw3sp.exe if there is one still in cod4 directory
make a copy of iw3mp.exe
rename iw3mp – copy.exe to iw3sp.exe
Make a shortcut of cod4 from the steam library
run the game as normal or through the fabled MP desktop shortcut !!
NOTE:Choosing Singleplayer will now take you to MP everytime, so if you want to play singleplayer just use the backup and replace.
Alternatively most people just make a shortcut to the iw3mp.exe but you wouldnt have steam integration, so it wouldnt track all those hours played or have overlay sometimes.
Also for other cool tweaks like 120fov go to this vid: