A recent entry in a lockergnome blog caught my eye as I deal with this similar problem almost on a daily basis.
Personally I have found that if I am spending more then 2 hours on a problem such as this, I will do the reformat routine as well. Thing is I don't just reformat, I go through the process of creating a backup "image" usually on a seperate partition of your hard drive if the drive size it large enough. Otherwise, I'll create this image to a network drive that I use for backups and then once the reformat/partition is done and windows has been reinstalled, I will restore the DATA ONLY which includes such things like "my documents" your email (identities), your address book and any other "obvious" program data files I can find. Usually this is enough as my client will then simply reinstall whatever programs/games they have that they want to use.
One good thing about this method is that it is like doing a spring cleaning on your computer.. getting rid of the stuff you no longer use which is key when dealing with computers that have children using it with all the learning games which are now out of date as the kid is a teenager. The teenager is usually in to downloading music and chatting on as many messenger programs they can find. As well, usually KAZAA is installed which is pretty much a guarantee that I will be finding viruses.. Word of advise DON'T INSTALL KAZAA!
