Anytime you migrate a GroupWise system from one system to another - and btw this could mean NetWare to NetWare, NetWare to Windows, Windows to Linux... It doesn't matter. You just copy the full GW folder structure to the new system. It's just files.
One caveat is with Linux, everything has to be converted to lowercase, so you use the dbcopy utility with the -m switch to handle this for you.
We migrate systems all the time, and we literally plop a system up from one server and down onto the other. Reconfigure the paths / startup configs, and we're off to the races. When you do it like this, all of your mailboxes, calendar, contacts, etc stay in tact - you haven't changed anything so why would they..
A great tool to use (assuming LInux is not in the equation) is Beyond Compare. Do an initial transfer, compare source and destination.. then when you're ready to make the cut, do a final sync.
You can find a presentation I did on my website that goes into this in quite a bit of detail and you should find very helpful..
Note that you need to copy your Domain structure as well as your Post Office structure.. Then you typically just reinstall the Gwia and Webaccess.
Good luck.
Marvin Huffaker, MCNE
Marvin Huffaker Consulting, Inc.
A Novell Platinum Partner