Sure about that? My guess would be more that the optical drive on the unit is dodgy. Near certain I had an 04 iBook G4 that was able to read DL discs without any issue. I'd have to double check to be sure, but I don't think a drive needs anything special to READ a DL disc. Write would be another story, but not sure about read.
Anyway, if you have another computer around, even a PC, you can dump an image of the disc to an ISO, and then with a little searching you should be able to find a website or two talking about how to reduce the thing down to what can fit on a single layer drive. Though I would be sure to check the optical drive on that unit with regular DVDs before wasting the time.
Wow I'm new to mac's and so far I can't hardly refrain from chucking this piece of crap out the window. Just bought this G5 and its only 3 years old. It has os x version 10.4.11. Well for some smart reason I can't run any of the apps I want to without having 10.5 leopard. I've tried installing leopard but the ******** (super-drive) doesn't read DL DVD's. I've searched everywhere for a solution to this....but nothing. Apple really drop support after 3 years? I'm going insane...Please help someone.... Thank you