I put the cod4-client-manualinstall_21.1 folder in the Mods folder, and I ran the install.cmd file, but when I ran cod4 from Steam, I got only one server, as shown in the below screenshot.
and install the patch on top of it, so you can play on cod4x servers without any problems. (search the internet for pirated iw3mp.exe and just paste where you have the steam game installed and install the patch again)