The password can't have any alt+ chars in it I do know that much. What os? Also if this is on Vista or 7 make sure you haven't installed into the program files or documents and settings. Did you run this as an elevated command prompt?
I would but this is my mother in laws new computer Xmas present and i had a rough time trying to format the drive to install win7 in the first place..... but that a different thread for a different time. I just figured why not put the computer to some good use for the next month.