I just upgraded to Windows 11 and had to change my hard drive. So I am in the same boat as Senzei.
I downloaded COD4 from Steam and have downloaded the patch to go back to 1.7.
I found this path
C:\Program Files (x86)\Steam\steamapps\common\Call of Duty 4
So I tried to install the patch here and get the error message
Setup has detected that you have a digitally distributed version of Call of Duty (R) 4 - Modern Warfare (TM) installed. Please refer to your original vendor for a Multiplayer Patch compatible with your version of the game.
Any suggestions?
Sincerely, dazed and confused..