Always have a backup of your stuff.
In general, upgrading from windows versions is not as "clean" as reinstalling from scratch. Especially if you are going from XP -> Vista -> 7 -> 8. Good for an academic/computer science exercise, but from a practical production system standpoint, just back your stuff up, and re-install direct. It's usually faster, easier, and produces a more stable system.
The finest tools are forged from the hottest fires