I'd just reformat.
Honestly, I do it almost every 6 months or so... just to keep things working at peak speed. Only takes me about an hour and a half to do a full reformat these days. I got all my installers backed up and all the windows updates on cd's, lol!
Edit: By the way, a really cool utility for windows that i have started to use when I gotta do work is the UBCD for windows.
http://www.ubcd4win.com/ 
