Since I couldn't find any information on how to do this, I had to figure it out myself
I think the following instructions will work on most laptops, but can't promise that it will.
Why is there no way to configure power-off in the screensaver dialog in Gnome? Well, it seems like Gnome can't detect that the computer has dpms support built in. This is probably because laptops has a very sophisticated power management already built in. I will not mention that KDE handles this just fine.
But anyway, assuming that you are using xscreensaver, which installs with FC5:
In your homedir, there is a file named ".xscreensaver". Notice the "." (the dot) in front of the file, which tells you (and the system) that this is a hidden file.
Open this file in your favorite text file editor.
Find where it says "dpmsEnabled False" and change it to "dpmsEnabled True"
Then, change "dpmsOff 0:00:00" to whatever value suits you. The format is H:MM:SS.
Make sure the "timeout" and "cycle" settings has values that will make them "kick in" before the dpmdOff value, or it won't work.
Restart X, and watch it work :-)
So, how can we power off the monitor if the computer is left in the login screen? After all, the settings we just changed applies only to the logged in user.
Here is how:
Edit the /etc/X11/xorg.conf (must be done as root).
In the "ServerLayout" section, add this line:
Option "OffTime" "5" (5 mins. timeout)
In the "Monitor" section, add this line (if not already there):
That's it. Did it work?