I'm toying with the idea of using Imoen's portrait in BG2 for my BG game. Is it simply a cut and paste job (drop the BG2 portrait into the Portraits sub-directory)?

No, if I recall correctly Imoen's portrait cannot be chaneged. Since she is not a character that you created, so this option will be disabled.
But indeed, it would just be a cut and paste job. If not, you can always print screen and cut it out and make sure you make 2 files of it, the big one and the small one.

Maybe it is possible in a multi game, but I dont know for sure..

I you know a way to evade what I previously said (hex editors could maybe do it), make sure you have got the dimensions right. 110 x 170 for the big one, and 38 x 70 for the small one. Also, I believe the filename cannot be to long.

However, I dont know why you should do this. I tend to like Imoens BG1 portrait better as the second one.

[ 03-08-2002: Message edited by: Validus ]</p>

You can use cut-n-paste (make sure you get the dimensions exactly right, check the readme file), or extract them with TeamBG utilities. If you want to use them for a PC, put them in the portraits folder. If you want to replace Imoen's portraits, name them IMOENL.bmp and IMOENS.bmp and put them in the override folder.