First, what backup software are you using...? Is this backup software Exchange friendly...? For instance, I use Veritas Backup Exec with the Exchange 2000 agent and this will backup and restore the entire M: drive, all Mailboxes and individual mailboxes if needed. If you backup software supports Exchange 2000, then it should be able to restore the M: drive to the state from the last good backup.
It is possible that you will have to also restore the system state for Microsoft Windows server active directory. This is another whole process that you have to do in Safe Mode and select the Directory Servicdes Restore Mode from the Boot-up Menu ( Hitting F8 before startup).
You can also search Microsoft's knowledge-base by going to
http://support.microsoft.com
Good Luck !!!