I'm sorry to read about the theft and hope that you are successful in getting the PC returned to you and the thief apprehended.
The local law enforcement agency with an active case can contact Microsoft and request this information officially. Law enforcement has a special number to call (I do not know this number) and they will need to take care of the legal paperwork to make the request. They will need to know your subscription information, PC name, and other information related to the account and that PC. I don't know if the information is available, but it is in theory.
-steve
Microsoft MVP Windows Live / Windows Live OneCare & Live Mesh Forum Moderator