Bad DVD

I bought the ORA "Photoshop CS4 One-on-One" Book / DVD package.

The DVD that came with my book is bad. During playback, there are frequent pauses and dropouts, so bad that it is really unusable. I copied the DVD to a new DVD+RW, same thing. I copied the videos to my hard drive, same thing.

I am a subscriber at Lynda.com and the Quicktime videos there play smoothly on my machine too, so I doubt it is my hardware (Vista 64, Intel Core 2 Quad processor, 8GB RAM, two 320GB hard drives, Nvidia 9800GT video).

Upon close inspection of the data side of the DVD, I can see a faint line running from the outer edge all the way across to the inner edge. I am sure I didn't scratch it.

How can I get an undamaged DVD? I can download an ISO image and burn a new DVD if the ISO can be made available somewhere.