DVD-RAM in older PMac?

A friend gave me the DVD-RAM drive out of his Blue & White. Today I
found a couple of bargain discs in cartridges ($1.00 each), so I plugged
the drive onto my PM 7500 (it has a PCI adapter for ATA drives).

The drive will mount the cartridges and Finder will show a window from
them (empty), but claims that the discs are locked, and I cannot write
to them. I've checked, and the little plastic "switch" indicates that
they are not locked.

The discs are "Single Sided 2.6GB TYPE2".

So, am I missing a driver (which one?), or will the drive just not work
on this Mac? I have Toast 5; will that burn the discs?

If I stick it in my Blue & White OS X 10.4, will it work with these
discs?

Isaac