wake on lan - Win 7 - XP

Please bear with me as I'm very much new to this. My laptop run on Win 7 and my Desktop (server) runs XP. The network is already setup to work with in the office. My desktop is connected to a modem and my laptop connect wireless to the desktop via the modem. I use my laptop from time to time in the field and than needs to connect to my back end db that is on my desktop (sometimes the desktop is off due to power failure or when it is shutdown I want to start it remotely). I downloaded WOL but do not know how to implement it. Must I install WOL on both computers

Please help me through the steps

The link below explains the Wake on Lan process pretty well.
Wake On LAN through your LAN or the Internet