To adjust the various system preferences from the command line you need the systemsetup utility which ships with OSX Server although I’ve found some versions of OS X client have it installed in /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Support. On my G5 with Tiger (10.4.8) installed I used systemsetup-tiger and on my iMac (Intel) that was missing so I used systemsetup-panther which also worked.

You can adjust all sorts of things with the tool -help shows you all the options, I wanted to adjust sleep times. Below is an example session, showing the settings before and after I had made the change

# ./systemsetup-panther -getsleep
Sleep: Computer sleeps after 10 minutes
Sleep: Display sleeps after 10 minutes
Sleep: Disk sleeps after 10 minutes
# sudo ./systemsetup-panther -setcomputersleep 60
setcomputersleep: 60
# ./systemsetup-panther -getsleep
Sleep: Computer sleeps after 60 minutes
Sleep: Display sleeps after 10 minutes
Sleep: Disk sleeps after 10 minutes