Yes, the computer are joined to the domain. However, the SCCM-client are installed, but not configured properly. I`ll resolve that problem first to see if the restore process also are resolved afterwards.
Update: The SCCM-client issue are now resolved. I tried a new offline migration from XP to Win 7, but still the same thing happens. No data restored. When I access the C:\USMTOffline folder I get an "You need permissions on this folder to continue" message. When I press Continue I can see the contents, but I guess I`m then taking ownership. Could permissions be the issue regarding the USMT restore process?
Update #2:
FYI I created a thread regarding the issue here:
http://social.technet.microsoft.com/Forums/en/configmgrosd/thread/d4fdfb19-1c24-417b-8b33-0d64af72dda4