I had a similar problem with two of my macs after I updated to OS 10.4.9, specifically a G4 flat panel iMac, and a 15" G4 Powerbook, except in my case I could not read any movie DVD and most burned DVDs. CDs worked fine.
I tried updating my iMac G4 to the 10.4.10 update, but that did not solve the problem. So I booted off my original Tiger 10.4 disk and used the "Archive and Install" option to reinstall OS 10.4 from scratch. This was a bit of a desperation move as a lot of applications install things into the system library that will not be there anymore after the reinstall (though you can retrieve them from the archived system or simply reinstall them if you have the original disks).
Anyway, the process worked and my DVD drive worked as normal after the revert back to 10.4. (That is, the drive could now read all disks including movie DVDs again.) After that, I installed the combo updater to OS 10.4.10 (i.e. skipping all of the incremental updates including OS 10.4.9) and the DVD player continued to work as normal, I could still read movie and burned DVDs without any problem.
As an additional bonus to performing this process, my iMac works better and faster than ever now. My iTunes 7.3 could not play movies or videos for the longest time without skipping so badly it wasn't worth the effort. Now they play wonderfully and smooth. I think I can put off buying that new iMac for awhile now. I have yet to try the process with my Powerbook G4, but I will as soon as I have time to back everything up properly.
Message was edited by: patriotusa