Thanks to Christian's provision of a SCSI cable, I've been able to get a DLT drive going for Peaceworkers. The drive itself came free from Freecycle. I'll be a lot happier knowing Peaceworkers are getting proper backup.
So now we need to get it installed into Peaceworkers and get them some tapes. Anyone got a cheap source for tapes? They're DLT IIIxt which are 15 (30 if you use tape manufacturer arithmetic) gigs. They'll need a cleaning tape too.
This is the first time I've really messed about with tape drives under Linux. Not entirely obvious or well documented, but fortunately my brother was online to point me in the right direction. Once you know the basics, it's quite easy.