Are you literally wanting to play online with other people or just set up a multiplayer game so you can create all your own characters?
The other person who was having this problem with a cable modem just wanted to set up his own party.
I set up a multiplayer game for him (not taking on any NPCs - left that to him) and emailed it to him. He then unzipped it into his save folder and replaced my chars with his own exported ones. Hey presto!
If this is your intention - I still have the save game file - I could send it to you if you wish - just drop me an email putting Baldurs Gate in the subject.
If you are wanting to play online I would suggest you contact Support@Interplay.com - they may be better able to advise.
It must be something to do with cable modems.....
