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Some users have reported that brand new Leopard discs are failing to mount(simply ejecting on insertion), on certain machines (Powerbook, MacBook, Mac Mini) even though the disc is seemingly flawless. Calls to AppleCare have resulted in Apple suggesting either creating a disc image and burning a duplicate disc, or the customer being issued a replacement disc. I was able to get around this by using a little bit of brute force and a little bit of finesse.

Work-Around Solution
1. With the Machine on, make sure there is no disc in the drive.
2. Initiate a restart, when the machines display goes to the “blue” intermittent screen right before it restarts, insert the disc.
3. Now that the disc is inserted and accepted hold down the “C” key on the keyboard and the Leopard install screen should boot when the machine comes back on.

Please leave comments if this worked for you.