So borderlands it turns out is a bit arse when it comes to network play

Ports need to be port forwarded as per this article
http://ad.gamersky.info/@forums.steampowered.com/forums/showthread.php?t=998836

and here are some tweeks to make it a bit nicer note the tweek to disable the ingame mic since we use ventrillo (cant be done in game)
http://gbxforums.gearboxsoftware.com/showthread.php?t=79043