I've been through a tense 90 minutes. My CD download got stuck on the last track ad would not complete, so I ended up shutting down the computer to elect the CD. After that, the computer would not restart. After 4-6 attempts to open it, I called AppleCare and spoke to a wonderful technician named Adrian, who talked me through several deletions of files, and finally got me back up and running smoothly. All is now good in iMac land. I just downloaded the CD again and everything went through.
Big sigh of relief!