could check out amanda community edition, can't beat free. I've heard a few good things about it but never tried it myself. They do have a paid version of it with support as well.
Amanda Open Source Backup
I couldn't find any mention of whether or not it would support your tandberg tape drive, but there is a 'customer comment' type thing on the right that says "Cycorp has been using Amanda for over 7 years now. In that time, we have scaled from backing up a few Gigs to a DLT 2000XT drive to over 2 Terabytes with an SDLT600-based autoloader. "
so you might be in luck