USE NORTON GHOST! (or a similar program)
Do it when your system's up and running fine, and if you get problems later, it can overwrite the config with the old, working one. (back up your documents beforehand)
Saves having to go through the OS installation process and the application insallations which can take hours. Lets you create the backup as a file so you can move it to another disk or even onto CDs.
This is for those who don't know about it. It could save you hours!