The thing to remember with Exchange is that the security of exchange is directly tied to the SID (Security IDentifier) of the NT/2000 server it is installed on. If the databases are restored to another machine (ie a disaster recovery machine), because of the different SID, the security will not allow access to the databases without modification.
If you have a backup of the origional machines system state, this can be restored to the new machine (as long as it has the same ID, IP, etc...) in ASR or recovery mode, restoring the origional SID. This will make things easier when accessing the databases.
Remember, two machines with the same SID can not exist on the same network!