Cloning, Imaging and Backup

I have a couple of questions as to when to clone and/or image a disk for backup.

After reading numerous threads, it appears that if a win xp backup was made via the "disk image" route and the computer from which the image had been made failed and needed to be replaced, then the disk image would essentially be useless (since Sysprep and/or cloning was not performed, the image could not be restored).

So, if the above is true then:

1. Can one perform a Sysprep and the simply "image" the disk or does Sysprep imply that you have to "clone" the disk?

2. Does all this mean that one should both image and clone (with Sysprep) in order to guarantee that a backup can be restored under all conditions?

3. Under what conditions will xp activation have to performed? I assume only on a clone with Sysprep.

Thanks,
Harvey