I had savecrash everytime after big battle. when I hit "save as" game ctd. but when I go to tavern then to town and talk to people and save game hitting F12, game save without problems. When I want to change save file I hit "save as" instantly after loading a game and select other savefile. I used this "savestrategy" on 10 saves and it worked on 100 %.
Edit: my specs - intel pentium dual core E6500 3ghz ,ati 4670 1gb, 2gb DDR2 ram , win XP 32bit SP3