I had the time and nerve to re-do this experiment. I did it on my older hard
disk as well as in a virtual machine in Virtualbox.
I set upa Windows 2000/Ubuntu Hardy Heron dual boot and reinstalled Windows
2000. The surprise was the dual boot persisted OK, Windows as well as Ubuntu
could be loaded with no problems. I reinstalled Windows 2000 again and the
result was the same. The dual boot scheme remained intact, GRUB did not have to
be reinstalled.