Hopefully there won't be much of an outage.
I'll need to use the maintenance page for a while before hand and take a backup of the database.
It will be quicker that way, as rather than copying the virtual server file across (20GB, approx 30 minutes to copy)
Instead I can back up the database, compress and copy that (tens of MB) then restore it and have us back up before you can say Jack Robbinson
Well, that's the theory.
First step is to get the domain controller back up and running on the main machine, and then move the groups that I moved out, back into the Users OU.