forgot admin password in vista, want to change it but it asks forthe old one!

My wifes laptop (dell) has a fingerprint reader, which she uses all the
time, until tonight when it decided to stop working. For the life of her
she could not remember what her password was, and finally after a reboot
it let her in. I told her to change her password immediatly for when
this happened again, but when she tried to it asks for her old password
in order to change it! What kind of crap is this? I then tried to change
it with net user <user> <password> and all I get is access denied. How
in the world is she supposed to change her password if it is insisting
she enter her old one? If she remembered her old one she wouldnt need to
change it!

I don't use Vista, in case you haven't guessed, I call it the ME version
of XP, which at least is a decent MS OS..