Find a PCI SCSI card that will work under OS 9 and install it into the G4
Boot the G4 into OS 9, load the original software onto the G4 and recover ALL your data from the Tapes.
Large FW drives would also be handy to store this stuff until you can back them up again using OS X, Retrospect and a DVD or three.

A review of three tape drives, one of which uses Travan tape can be found here.
Hope the above, and below, help.

http://www.macworld.com/2001/02/bc/28reviewsfirewiretd/

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