Here's a utility that claims to be able to pull the install keys from a non-booting drive:
http://www.mayhemdevelopment.com.au/products.php?prodID=827192:
Quickly recover your products keys for windows, office and exchange. Windows 7, Vista, XP. Office XP, 2003, 2007. Recover your products keys from a system that will not boot with added support for external files.