Skype Video Audio Call Over LAN - Possible?

I'm wondering whether Skype can make calls over the LAN. What I know is that the software uses similar technology like Kaazaa and it should be possible to make calls over LAN, but I don't seem to figure out how. My setup consists of a wifi router that connects two computers each installed with Skype. I'd like to skip Internet and use the local area network to make a call - say from room A to room B 😀

Does anyone know the trick?