I just tried doing the Repair -- as well and an 'over the top of' -- Vista installation and they both failed.
The reason: "Recent .... hardware change may have caused the problem."
For that particular HDD, I may have to see if there's a way to get that other motherboard to boot at all. I really do want to get to my data in the Documents and Settings directory. That's really my only BIG concern right now. Never thought they'd lock that up tight as a drum.
EDIT/UPDATE:
Aha! I don't actually NEED access to the Documents and Settings directory after all. All I really need is access to my "USER" directory and then proceed from there.
Hopefully, once I get things backed up, I can format this drive and install Vista afresh. (Hopefully, with fingers crossed.)