Sorry to hassle you,
But is it practical for you [that is a restore point less than two weeks old] to use the RESTORE point of Vista to Pre-GWX/ Pre-SH3? If so, uninstall SH3, goto the SH3 folder in Documents - delete it, then use the RESTORE point and give another try on the reinstall?
PLEASE be very carefull on our advice. I'd feel more comfortable that you had a TOTAL backup of your rig BEFORE trying ANY of this.