Parallels 6 upgrade of VM taking forever

I just upgraded to PD6 from PD4. My 1st-gen Mac Pro has been grinding away at upgrading my XP virtual machine for about 6 hours so far (as I write this). The "modified" date of my 21 Gb "Windows XP.pvm" file updates every minute, the Parallels upgrade window constantly cycles through its various tips, the Parallels icon in the dock shows a slowly spinning set of activity "spokes" and I hear disk activity (no other application is running), all of which suggest that the application is doing something. But the progress bar at the top of the upgrade window has been stuck at about 25% of the way through "step 1" ("preparing to upgrade...") for hours. Furthermore, I cannot open any other application; nothing happens when I try. I tried to close the Parallels window, but I get a warning not to quit while the upgrade is in progress.

So to my question: is this normal? If so, how long should I expect this to take?