Hi Phil,
You can move the .MDF (database file) and .LDF (log file) files to another drive location. This can be any sort of drive that is attached to the network. (USB, NAS, SAN etc)
Please refer to the following KB article on our forum that explains how to move these files
http://forums.exclaimer.com/forums/thread/2339.aspx
With regards to the new server, as long as the AD is not changing, moving to a new server will not cause any problems. If you are installing new DC's you will need to migrate the AD to ensure users can view their messages correctly. The database records will not match if you recreate\copy the AD.
Best Regards
Joshua Clarke
Exclaimer Support