I was browsing around and saw this thread. Have you tried burning your install disc on the slowest setting possible?

My burner reports around 4-5Kbps with settings like "slowest" or "low" (transmac, a program I often use doesn't show the x1 etc speeds for burning.) I believe I have made successful back-ups of my retail install DVDs by burning on the slowest setting supported. I hope this helps.