Have you tried seeing if the 'light' version works at all? how good is your PC/laptop? people with older versions might be getting slight performance issues with the mod...
Parrot, you got any suggestions as this guy has been trying a while now and things are getting weirdly silly.
Could me verifying the game cache through Steam have done something to not make the multiplayer solution work? Btw, Lite version doesn't work either :/
My PC has an Intel i5 processor and 650 at 3.20GHz, and it's 64-bit.