My final mail on this:
After trying all combinations of cloning and restoring that we thought might help, we gave up on trying to do this the smart way and made our copies the tough way.
So, what we did successfully:
1. We created one master system with XP and its applications on C, Vista on D, and shared data on E
2. Using Acronis TrueImage 11 Home we made a copy of the XP-partition on a USB-disc
3. On the new systems (the clones) we restored the XP-partition; not the MBR or track 0
4. On the clones we used Partition Magic to create the partitions.
5. We installed Vista in Partition D
6. We installed the Vista applications in partition D
7. We copied the data to partition E
8. We finalized the settings and Faronics Deepfreeze
9. We used VistaBootPro to change the start-up prompts and default
10. Steps 3 thru 9 were repeated 9 times (for each of the clones)
In retrospect: TrueImage turned out to be good for XP; at least we only did everything once there. My feeling is that either TrueImage has some flaws with Vista and dual-boot and/or with the combination with Faronics Deepfreeze.
I have reported the problem to Acronis.
This was a one-time action, so my interest in solutions is academic from now on.
Thank you all for your support!