Vista - Force user logoff from Task Manager

Hello,
Being a long time user of windows XP in a PC with severeal user accounts, I
was used to logoff active users from my administrator account.
However i find that is not possible in windows vista. I'm a trying to log
off a limited acess user from the task manager in my administrator account,
but the system says it is not possible. I have to switch to the other user
account (it is not password protected) and log off from there, and then come
back to my account to be able to finish what i am doing, (unistall software,
etc...)
Is there a way to force the user to shut down from the task manager in
Vista? Am i doing something wrong?
Best regards,
Duarte