I think that this is because to restore AD (the ‘system state’) it needs to be the same machine (as in GUID’s) or all kinds of proverbial will hit the fan. It gets further complicated with AD and tombstoning. However from the sound of it you are looking to do a ‘Authoritative Restore’ of AD.
You can restore the system state (where the AD DIT file is) just to a folder so that you can take the required files manually.
Then go to your server and start it up and get a blank AD in place. Then start up the server in Active Directory Services Restore Mode (F8 on start-up). Double check the Domain controller has all of the roles it is going to need then using the command line use ntdsutil to do a ‘Authoritative restore’ of AD (authoritative means that this will override all currently stored AD data and replace it the incoming data, if you just want to add to what you already have in AD use a non-authoritative restore) and point to the location of the .DIT file.
This is more or less it. I suggest spending a few moments to run through the process on the microsoft technet site.
You can also find out more about ntdsutil here (including commands and switches)