I want to transfer Vista & XP from seperate HDD's onto a main one and I don't have the system disk of either OS. So, what's the difference between the utilities in the title? Which is easier to do?
Imaging/cloning is what you need. Backup/restore is not generally so good (particularly for XP) for restoring an entire system (but much better for restoring individual data files).
Cloning is by FAR easier if you have access to norton ghost. You could partition your main drive into two partitions, clone each drive onto those partitions. Takes no time at all and very easy to do. If you dont ave access to norton ghost, try something like clonezilla (open source), ultimate bootcd, and i beleive easus has a disk cloning/backup solution as well.