This is blatent copy-paste job from: http://rotwhiler.wordpress.com/2009/03/24/enable-wake-on-lan-through-linksys-wrt54g/ put here for my own posterity.

This all works very well if the computer sending the Magic Packet is on the same LAN as the sleeping computer, but requires some additional effort to get working over the Internet. Especially if the very common Linksys WRT54G is your wireless router. The WRT54G setup page employs javascript to prevent the user from entering a broadcast address, so there is a work around. Here’s what to do to set this up:

• Enable WOL on your computer. This is usually a setting in the BIOS. (This may not be possible if you are using a wireless card. Only the very latest cards support Wireless Wake On Lan.)
• If you don’t already have Firefox, download and install it.
• Download and install the DOM Inspector Firefox Add-on.
• Using Firefox, open your Linksys WRT54G admin page (usually 192.168.1.1)
• Click on Applications & Gaming
• Add a new entry: Application=”WOL”, Start=”9?, End=”9?, Protocol=”UDP”, IP Address=”200?
• In Firefox, click on Tools, then DOM Inspector.
• Use DOM inspector to find the “WOL” entry and change IP Address from 200 to 255. (Firefox will red highlight the areas you have selected in DOM Inspector, this makes it easier to narrow down to the correct element.)
• Click “Save Changes” on the Applications and Gaming page.
• Download and install a Magic Packet program that can send a packet over the Internet. I like this one: http://magicpacket.free.fr/

You should now be able to wake your computer up from where ever you are. (Also, I should say that my router has firmware version 8.00.5. I don’t know if this matters, since I don’t have any other router to test it on.)

Note to self: this is probably unsafe and bad. Also, I used firebug.