To run SD! on 10.2.8 you'll need an older version; a download link is under
System Requirements in the right column of the
SuperDuper! page. That's probably the easiest/safest way to create a bootable backup of the internal 10.2.8 volume on an external volume, especially while this type of thing is still unfamiliar to you. Otherwise you'll need to boot from a 10.4 (or newer) volume to run the current version.