Shutdown after idle time?

Mint with Gnome-shell?
Section: Shut down or restart
http://library.gnome.org/users/gnome-help/stable/shell-exit.html.en

Or Gnome 2.32?
http://library.gnome.org/users/user-guide/2.32/user-guide.html#shutdown

There're also several GUIs to shutdown at a certain time (at least for Ubuntu)
gshutdown
kshutdown
shutdown

Otherwise refer to Mint community, wiki, tutorials.
http://linuxmint.com/

Or via terminal:
e.g.
# shutdown in 60 minutes
sudo shutdown -h +60
# shutdown 8:30 pm
sudo shutdown -h 20:30
# manpage
man shutdown

In case of Xfce-session refer to their tutorials.
http://wiki.xfce.org/faq?s[]=xfce4&s[]=session#session_manager

Thank you for your immediate reaction. Unfortunately I can't find a solution to my problem in your answer.

I know how to shut down my computer; and I know that I can plan this manually via terminal or via one of the mentioned small GUI programms.

What I need is an automatically startet service, running in the background, which shuts down my computer after a defined idle time, eg. 30 minutes of inactivity. Gnome Power Manager does this job almost perfectly, but lacks an option to shut down the computer instead of using suspend or hibernation. Or maybe I can't find this option?

If there is no such option in the gnome power manager, do you know any other program or script that can do the required task for me?

Thanks!
Christian

Thank you for this. I will try and hope that it works.
I admit that I hoped for something more newbie friendly as an automatic shutdown seems to be a standard feature elsewhere.
Nevertheless, thank you.
C.