I just recently reinstalled BG1 to play it again with my new computer with WinXP. It worked fine until I went to Beregost and took Kagain in my party. After he joined the party went walking to Beregost, and the game crashed the whole WinXP, forcing a reboot. After one of the crashes I got a blue screen saying "Windows has been shutdown." I can't remember what the exact text was, but it referred to a possible device proble, which I thing is unlikely because I've never seen a message like this before. It always shows up in at least 5 minutes if I have Kagain. If I don't have him in my party, the game works fine.
Has anyone had the same problem? Is there a known fix (other then not using Kagain)?