You should ask him a few more questions like:

Is this computer on a domain? Is it a stand alone computer what OS are you running.

If he is stand alone with XP pro he could get to the log in screen and hit ctrl+alt+del twice to bring up the login prompt for the admin. Log into the admin which more than likely will be blank. From here he could change the pass.

Sometimes YOU are the admin=) hard to ask yourself a password.

On a side note who in the world forgets a password? I mean YOU created it