System Profiler
In your Applications folder (or somewhere within it) there's a program called System Profiler. Run that and look in the Hardware > ATA section. You'll find something like (but probably not exactly like):
PIONEER DVD-RW DVR-105
This is the model that came in my 2003 vintage G4 PowerMac. Depending on the model yours shows, you can check that on the web. For instance, the DVR-105 is a 4X DVD-R (no +R). I've since added a DVR-108 (non-Apple branded of course since they don't sell aftermarket drives) which is an 8X DVD+/-R.