Currently Being ModeratedJan 27, 2013 12:17 PM (in response to zipmac22)
Use the Disk Utility in the /Applications/Utilities/ folder to repartition it as GUID(or APM if you're using a PowerPC Mac) in the Mac OS Extended (Journaled) volume format.
Currently Being ModeratedJan 27, 2013 12:18 PM (in response to zipmac22)
If it was set up for SuperDuper, it should be Apple-format.
Go into DiskUtility, select the partition of the external in the left column, and you should have an "Erase" option at the top of the main-activity window. You can decide if you need more than simple "Erase" (you can do a 7-pass erase, but nromally that is used when transferring a disk to a new user/buyer).