I'm using Windows Vista.  I have set up several user accounts, one for each member of my family.  Only my wife and I have admin rights.  

There have been several times when my children "accidentally" leave the computer and after a certain amount of time, Vista "locks" their screen requiring them to enter their password to get back in.  

Unfortunately, I can't find any way to override their password with an admin password or account and get back into Vista.  I can't even find a way to shut down the computer from the locked user screen.

The only way I've been able to regain control is to do a HARD reboot.

Besides disabling the ability to put the system in locked mode, does anyone know how an admin user can unlock a locked user or even shut it down normally?

Thanks!