EDIT: I guess the official Steam update is up, please restart Steam to update 
Disregard the rest of this post
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I'm typing this at work so I don't know for sure if Steam has updated yet or not, but this is a pretty straightforward way to get the Steam version of COD4 patched to 1.4 without having to wait for th official update.
NOTE: This is a temporary fix. It breaks the single-player version of the game for now, so if you plan on playing the SP as well as MP versions of the 1.4 update, then you'll have to wait for the official Steam update.
NOTE2: ALWAYS ALWAYS ALWAYS Backup when doing something like this. To backup your game, open your Steam "Play Games" menu, right-click on any game in your "My Games" menu, and choose "Backup Game Files..." and follow the instructions. You can alternately "Verify your Gamecache" after you manually patch, which will supposedly revert your game to the last official Steam update, which at this point is 1.3.
NOTE3: This is an AT YOUR OWN RISK procedure because it involves a tiny bit of registry manipulation. It works (or rather, it works for me), but there are no guarantees outside of the official Steam updates. It's also probably a good idea to backup your registry, even though you are only changing one key, you don't want to risk doing more serious damage by accidentally changing something else.
How to manually patch the Steam version of COD4
Disregard the rest of this post
-----------------------------------------
I'm typing this at work so I don't know for sure if Steam has updated yet or not, but this is a pretty straightforward way to get the Steam version of COD4 patched to 1.4 without having to wait for th official update.
NOTE: This is a temporary fix. It breaks the single-player version of the game for now, so if you plan on playing the SP as well as MP versions of the 1.4 update, then you'll have to wait for the official Steam update.
NOTE2: ALWAYS ALWAYS ALWAYS Backup when doing something like this. To backup your game, open your Steam "Play Games" menu, right-click on any game in your "My Games" menu, and choose "Backup Game Files..." and follow the instructions. You can alternately "Verify your Gamecache" after you manually patch, which will supposedly revert your game to the last official Steam update, which at this point is 1.3.
NOTE3: This is an AT YOUR OWN RISK procedure because it involves a tiny bit of registry manipulation. It works (or rather, it works for me), but there are no guarantees outside of the official Steam updates. It's also probably a good idea to backup your registry, even though you are only changing one key, you don't want to risk doing more serious damage by accidentally changing something else.
How to manually patch the Steam version of COD4
First, close Steam.
Then go to start > run > regedit
Search for :
for XP & Vista 32: HKEY_LOCAL_MACHINE\SOFTWARE\Activision\Call of Duty 4
for Vista 64: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Activision \Call of Duty 4\
right click on "Digital Distribution" and rename it to anything else.
download & apply the patch from Infinity Ward's website:
http://www.infinityward.com/modernwarfare/patch/
Then rename the key back to "Digital Distribution"
Close Regedit, restart Steam, and happy fragging
Then go to start > run > regedit
Search for :
for XP & Vista 32: HKEY_LOCAL_MACHINE\SOFTWARE\Activision\Call of Duty 4
for Vista 64: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Activision \Call of Duty 4\
right click on "Digital Distribution" and rename it to anything else.
download & apply the patch from Infinity Ward's website:
http://www.infinityward.com/modernwarfare/patch/
Then rename the key back to "Digital Distribution"
Close Regedit, restart Steam, and happy fragging