Don't use the Veritas/Symantec drivers. Keep what you've got--if it works, it works. You won't have any problems with them.
I have a SuperLoader 3 with the SDLT600 on a W2K3 server and I use the Microsoft driver for the Medium Changer and the Quantum driver for the Tape Drive in the Device Manager. Works perfectly. Rarely have the Veritas drivers worked with my Quantum devices.
More info...
http://forums.symantec.com/discussions/thread.jspa?threadID=69638&tstart=30