The disk image backup feature on Windows is retarded. You'll be backing up and reinstalling the very files you want to destroy, since you'll be backing up all the caches and log files. You should individually backup the most important files, wipe the drive and do a clean reinstall of the OS, then copy the backup over. Get a thumb drive. Use Truecrypt to encrypt the whole thing. Copy over your important files. Yep, DBAN has a one-click nuke option, just make sure the thumb drive isn't plugged in or it will nuke that too. Install it from a normal installation disk, not a backup image of your drive. Key servers. If you don't know what they are, don't use them.