You aren't alone here.
http://forums.ubi.com/eve/forums/a/t...5/m/7691074936
I don't believe it's your system, it's just something new that v1.5 introduced for certain NVIDIA cards IMHO.
I found SP1 for Vista and it seems to have helped with this specific issue. I haven't played enough yet to be certain though. Before you do any further messing with your rig, wait until SP1 is officially released through Windows Update and give it a try.
Last I heard, SP1 for Vista is supposed to show on Windows Update on March 18th.