desktop hard drive to sleep/ power down

I’m using opensuse 11 on an IBM Thinkcentre desktop with kde 3.5.
I am trying to find a way to put my computer into sleep mode after 35 minutes of inactivity, so I can come back later and hit the space bar or mouse to wake it up. (or hibernate-anything to save power so the desktop is not running 24/7)
I tried setting this up in kpowersave but suspend to disk/ram does not work.