I recently bought a HP external tape drive, connected via SCSI to my G4
Which model of HP tape drive did you get? Did it include
any software at all; was it even formatted as a Mac HFS volume? Did the vendor know you wanted a Mac-compatible drive and sell this one to you anyway?
You may be able to use
Retrospect ($119) depending on which HP drive model you have. A download update for it adds support for these HP tape drives:
HP StorageWorks Ultrium 1840 (SAS) Tape Drive
HP StorageWorks Ultrium 1760 (SAS) Tape Drive
HP StorageWorks Ultrium 920 (SAS) Tape Drive
HP StorageWorks Ultrium 448 (SAS) Tape Drive
HP StorageWorks DAT 160 (SAS) Tape Drive
You may have to call or email them to find out all the drives that are supported by it. If that won't work for you, I'd return the drive for a full refund and ask them to find one that is Mac-compatible and comes with Mac drivers to mount it.
Mulder