Yes, I was left a Linux (Suse 10.2) desktop computer, and have had no luck in finding files so I can make it a dual boot system adding Windows XP.
Now I need to know how to make a backup of this OS so I can remove Linux, install Windows XP and then do the dual boot with Linux?

What do you mean by you can not find files to make it dual boot?

Depends on how the drive is partitioned to know how easy it would be to resize and install windows. Yes the current bootloader will be overwritten but it
is easy to restore. It is also easy to boot linux from windows.

partimage might be an easy way to backup your system as a beginner.

what? wow! no one has ever asked that! I honestly don't know how it's partitioned and I have no idea how to figure that out?
Maybe I've come to the right place! Up til now I'd been left with the impression that not having Windows already on the machine; well dang near impossible to make it dual boot and add Windows XP.

To list the partitions use the fdisk command
fdisk -l (that is a small L and you must be root)

The advantage of loading linux last is that you do not have to reinstall the boot loader.

Gonna have to delve deeper into my Linux books I can see. Big Thanks!