NOW IT WORKS!
It seems to have been a virus. While I was working on the computer this afternoon, my BitDefender virus detection box kept popping up saying it had found and removed a Trojan Horse virus. It would pop up every 20 seconds referring to removing the same file - qeolmc.pnn in the Windows directory. I tried to delete the file myself, but I couldn't because the file was in use. I rebooted into the Recovery Console and deleted the file manually via the command prompt. When I rebooted into Windows XP, both DVD Decrypter and Imgburn started with no problem
I must have had this virus on my system for a couple of weeks now, because my computer has been acting a little weird. I guess the latest BitDefender update finally recognized it as a virus and tried to kill it. It must be fairly new - I did a Google search on this file name, and came up with no hits.
Anyway, thank God Imgburn is back, and thanks for your help.