no, they will read any - or +R disc if finalized. after that it's readable on any DVD drive that can read burned discs. It will only burn +R or -R if it supports. Once it's finalized, it will read any format.
Chances are the laser is out of focus or is dying (it could either be the laser or the receiver) which will require you to replace the drive, or if you are daring, get in and adjust the lens or laser intensity.
Try to boot off another machine with Firewire target disc mode. you can use another desktop or laptop with firewire built in (except the Yikes!/B&W G3 which isn't onboard). Try like an intel mac laptop or powerbook. Pop the DVD drive into the laptop, boot it with the "T" key held down and connect a 6-pin FW400 cable between the laptop and the iMac. Hold down the option key on the iMac and select the disc.
Install from that.
Chances are the laser is out of focus or is dying (it could either be the laser or the receiver) which will require you to replace the drive, or if you are daring, get in and adjust the lens or laser intensity.
Try to boot off another machine with Firewire target disc mode. you can use another desktop or laptop with firewire built in (except the Yikes!/B&W G3 which isn't onboard). Try like an intel mac laptop or powerbook. Pop the DVD drive into the laptop, boot it with the "T" key held down and connect a 6-pin FW400 cable between the laptop and the iMac. Hold down the option key on the iMac and select the disc.
Install from that.