So here's the issue. Three computers, two running Windows 7, one running Vista. We can start the game in windowed mode and through that we can host and join games, no problem.

What the problem is that once we start the game, all computers but the host instantly disconnect and all characters are erased. They are replaced with two characters that were allegedly created by my brother and his friend years ago but which they never saved (our discs are too damaged for reinstalls so we spread the game from old computer to new computer via USB).

Anyone have any idea what could be happening here? Is this a port forwarding issue or something?

My friend and brother and I love this game like there's no tomorrow and being able to play it multiplayer again would be incredible so any answers anyone could have would be hugely appreciated

Let me make a wild guess. The host computer is where the original install of the game is, correct?

From the sounds of it (and i'm no expert, so if anyone has a better idea/solution, feel free to post away :p ) the other players are getting disconnected from the game when the host starts it up because they are missing some essential game files or something. If any/all players disconnect, the game install itself might be damaged or something. As for the characters being replaced by those from a previous playthrough, i'm not too sure how exactly BG handles this aspect, but it's possible that the characters that replace the new characters are coming from an old save.

Have you guys attempted to start the game in single player? does it crash, not start or anything? or does it work fine?

I would suggest a re-install of BG after verifying the above, but since you mention the game CDs being too damaged to be used. Copy the entire BG folder to the other computers just in-case some file(s) didn't make the transfer, got damaged in the process or whatever.

It could also be that the game needs to make a registry key, entry or whatever or modify an existing one during the installation procedure and since that is being bypassed when you simply "copy and paste" the game folder, you guys are thus getting the problem you are describing.

Don't worry or even mess around with your network, if everyone can join the host's game, then your network(s) are fine, otherwise one or more players would not be able to join at all.

These is all guess-work and assumptions, i might be rambling useless things, but since nobody has tried helping, i figured i would :)

Hope it helps...and if it doesn't, you guys could always buy the GOG version ^_^

Thanks very much for your help! BG1 Tutu works perfectly fine, so I suspect that one of your answers would be correct. I also have several mods running so I might try re-installing some of those (or even un-installing).

I'll let you know what happens. BG1 Tutu should tide us over until we figure it out (plus in my opinion it's the better one for multiplayer anyway as it's less plot-heavy at the start)

EDIT: Also, the interesting part is that the characters appearing do not appear in any save games. My brother and his friend confirm to having made them years ago but abandoned the game almost immediately to go swimming (or something). So they haven't actually got any save games or character files anywhere and seem to have been pulled from some bizarre computer space.