I found this the other day when I found that I had to re-install Windows XP in my emulator - it's not a crack, it's not illegal, and it doesn't break the license agreement. All it entails is retrieving two files from the old install before wiping and re-installing, then placing these two files back in the same location in the new install. Very simple to do!
Here's the article:
http://news.softpedia.com/news/Manua...ft-59142.shtml
I did this because my install had been got at by trojans and a virus (or twenty!), and my Windows XP disc and key have reached the limit on re-installs. Despite my old install having viruses, the two files I retrieved were scanned and passed virus checks OK.