Paul

thanks for your response Bo.

When I attempted to open the VMC on the 2nd machine it responded that
files were "locked" by another machine. I assumed thismeant the VMC
knows about the hardware it expects.

When I copied the VMC and used this one it worked, however it created
a new undo disk and would not allow me to merge this when shutting
down. Therefore when I moved the disk back to the original machine
and opened the original VMC, it knows nothing about the undo disk and
simply starts the VPC with it's own new undo disk.

Therefore I can get both VMCs sharing the same base VHD, but just not
both being able to use the same change set.

It sounds like what you are doing is exactly what I want to be doing.

Maybe it's Vista not allowing Admin access to the files as I am
appearing as a different user on the 2 physical machines?

regards,
Paul.