Alternatively, you can also use Deep Freeze by Faronics. Doing crap with your PC, restart, and everything is as before.
Backing up your system - whether on -or offline based - seems to be a big topic here.
Old but gold-method: Put in your Windows-DVD, restart, boot from Disk -> Format C:\ and performing a clean-install is the safest way to get a healthy system.
Deep Freeze, or if you want the same but free, there's Reboot Restore Rx as well. I mean, why fork over the money for a program that's doing the same thing for free.
Well the resque cd/mode from bitdefender and kaspersky have a build in web browser. Firefox has a refresh option in "Troubleshooting Information" if a problem occurs.