When you start a multiplayer game, do you play it like a single player??? and do you need two computers??? can you play alone???

You can play a multiplayer game alone if you choose. The advantage is that you can create more than one character. One player multiplayer games play the same as single player games with the exception that you miss out a bit on NPC interactions since you'll have fewer NPCs in your party. Once you create a multiplayer game, save and exit the game. Copy the saves gave from the multiplayer save directory to the the regular save directory. This will greatly speed up load times.

Of course, you can play multiplayer with more than one person, and it can be fun if you find a good group of people.

Does every player in a multiplayer game need thier own BG2 CD´s.

Good question Tirk, I would also like to know that answer.

Yes everyone needs their own copies of the game. Although there are ways to do a full install and play the game without the CDs but this only encourages piracy. The NoCD patch can be found at http://www.gamecopyworld.com/

I use that patch anyway. Otherwise I have to sit here and listen to my cd-rom (aka the Jet Engine) the entire time I'm playing the game.

Thanks for the useful pointers