[jaycee]

Well most of the things you want to back-up are documents, so you just put those on your hard drive, and anything else you want to save. Then you could reinstall Windows, or try a Linux distro. (If you try Linux, you won't have to worry about viruses, even if that rootkit was transferred to the external hard drive...) Of course, if you're a gamer, you'll probably be forced to use Windows...