It's been a long time since I've seen them, but there used to be kits to polish the bottom of a CD to help with this kind of problem. The actual data is near the top side of the CD platter, so a modest amount of polishing can take place without damaging the data. Several folks have told me that polishing with toothpaste does an excellent job, apparently some brands have just enough abrasive to do the trick. Here's a link on home remedies: http://www.usbyte.com/index_recovery.htm#CD