The first thing you should do is make sure everything is backed up, twice. Once to another hard drive and one to a set of discs that you keep someplace else. Gas line burns your house down, nice to have a backup ata family member's house.

I have had a lot of good luck with CCLeaner (http://www.filehippo.com/download_ccleaner) It can do a lot of what people were saying (cleans out registry, gets rid of temp files in Windows and IE).

You may want to consider reformatting and reinstalling Windows again. After a certain point (and 6 years is WAY past it) sometimes there is just nothing you can do to get windows to run as fast as it did.

Good luck!