How to play MW4

Well, considering MW4 is a pretty damn old game, there have been many updates and patches etc. First of all, MW4 and all the XP packs will soon be released for free my MekTek.net. If you have discs lying around somewhere you can use those too I suppose, but the DL version will not have the CD protection and you can play without the disc in the drive. In the meantime, you can download all the updates and MekPacks, which include a ridiculous amounts of new mechs and weapons. You can also get the Co-Op mod for Mercenaries and HD Texture pack.

Get the patches and MekPaks here.
Get the HD patch for Mercenaries here.
Get the Co-Op mod here.
If you have all the XP packs you can get an updated Co-Op mod here.

After you are done, make sure to run the .reg file in your MW4: Mercs directory in order to change the multiplayer server to the one hosted by MekTek rather than the one by Micro$oft.