The disk cleanup didn't work, but it was a good idea that I hadn't thought to try.
Yes, I think you're right, the CDR image data has to be loaded in by Corel. I seem to recall, a long time ago, making a registry entry or correction when I had trouble on another computer.
But no, the system giving me trouble now is a 32 bit, not 64-bit. My 64 bit machine (a Gateway running Vista) is displaying everything just fine. I did have trouble with the 64 bit at first, but finally got it working.
An example of the silly tricks people play to make it work: The Photopaint (Corel's photo/bitmap editor) images wouldn't display thumbs on my Gateway, so I had to associate the files with an earlier version of the program still on the machine. That worked in for me in Vista, but not in Windows 7.
Thanks again for the time & trouble.