dunno if any of you have been following it but i have been for a good few years but flamekniight7 has finally release a working beta3 version of hte mod
i think it has a working coop as oppoesed to that glitchy coop mod which came out which only worked on version 1.1
http://www.moddb.com/mods/assault-coop
might have a try and see how it runs