DVD burner with an old iMac G3 - 333mhz

Hello there !!!

3 years ago i buy an USB Iomega CD-RW 48x24x48, and all this time the burner working right.

Well, i was thinking about upgrade to a DVD burner and use the case from the Iomega burner (replace the old CD burner inside for a new internal DVD burner). I talk with a friend to use his internal DVD burner to try that and then if working go to the store for my own burner.

The first time i install it, the Mac and Toast 6 recognize the drive, then try to burn a DVD. The burner begun, but minutes later Toast give me back an error comunication with it.

I try to burn again with a new DVD but Toast give an error about there's not blank DVD (i supose that's was a joke). Try so many times, but without success and the same error.

My iMac configuration is: 256 ram, 22 GB free HD, 333 mhz, MacOS 10.3.9.

My question: Is that possible because i have an old Mac and a low level configuration, the system don't support a DVD burner, or the real problem is about the Iomega case ???