Well, I know diddly about this, but if he can create a server, and actually start a game and enter it and play, but not join any other servers, that sounds more like a router/firewall/port issue than an OpenGL/video driver issue. You're saying that locally, the game runs. E-mail him the url for this thread, and tell him to register on the forums and post more information here about his problem. I think we need to know more, but maybe someone else can tell you from just the little bit of information we now have to go on.
Typically, we'd want to know the OS, a little bit about the hardware, and see a screen capture or the error code. What kind of wireless/router/network is he using, and how many other machines are on it?
