Firstly install Call of Duty 4 Modern Warfare and patch to version 1.7 if installing from game CD or if you are using Steam the version it installs breaks the online game. To resolve the Steam issue you will need to over write the iw3mp.exe file with the 1.7 version. We host this file and it can be found here
Once the above is complete then join one of our servers for example 18.104.22.168:1024 this should then start the automatic process of the COD4x upgrade. If this fails then please go to the COD4x site here and download the windows client. Once downloaded complete the following steps.
In 99% of the cases the in game method will just work, if you have any issues please post a help request here.