How do I create a sleep shortcut

Hi,

on my older 10.5.8 desktop G5, I was able to create a "sleep shortcut" in the Systeme Preferences, >keyboard& mouse > Keyboard shortcut and going into the "applications Keyboard Shortcuts" clicking on the triangle to get "all applications" or "Finder" and there (i dont rememeber how I did it) I have assigned the key F13 to sleep.

Now in 10.6.8, the access to Aplication shortcuts is slightly different to access to, but once there, I clicked on Finder, and clicked on the "+" sign to create a new shortcut, in the pull down menu "Application", I used "Finder", and in the Menu title I typed Sleep (S with a cap letter) and then pressed F13 key for the "keyboard shortcut" and I see the F13 key being entered aotomatically. But when I close the System preferences, the F13 key does not do anything.

Any idea what's wrong?

Michel