Requirements:
You should check the "wake up on administrative network access" in the Energy-Saver-PrefPane
Waking up:
There are several utilities for waking up computers over the LAN. A cross-platform utility is WakeOnLAN.You'll need the MAC-address of the computer you want to wake up:
% wakeonlan XX:XX:XX:XX:XX:XXTo get the MAC-address, ssh into your OS X machine or start the Terminal and
% ifconfig -aEvery network interface is listed, the ethernet-interfaces (en0) are listed with ip-address and MAC-address.
Putting it into sleep:
There is a command-line-utility called SleepNow. Download it and put the application SleepNow into a place where you can find it later. Log into your remote OSX computer and:
% cd [the/path/to/SleepNow]The remote machine should sleep now.
% ./SleepNow
[Editor's note: I tried waking our iBook via Airport using these methods (in both this and the previous hint), but had no luck. I'll try later using a hardwired ethernet connection as this would be quite useful to me, as I mentioned in the earlier hint's comments.]

