Originally Posted by Joshua Nightshade

Adam says yes, it's very simple.

You would just set your external IP address to your LAN one instead of the default (which is 127.0.0.1); when you first set your region up there's a prompt for it, or if you're editing a region that already exists you would edit the default.xml file in the Regions folder (which should be in the root directory or bin if you're using subversion to update).

You get your LAN IP from (if you're in XP) Control Panel > Network Connections > then right click whichever your LAN is and choose status. Click the Support tab and your LAN IP is right under Address Type. It usually starts with 192.168, on mine it's 192.168.1.200

Then to connect instead of using the default loginuri you would replace it with that address and you both should be able to connect.