Can anyone help me sorting out my pc issue..

I have a main pc as well as a laptop the main pc is connected to my router via the cable and my laptop is wireless...

how can i get the computers to see each other so i can play a game with my old man?

the router is a Netgear DG834GT
my main pc has vista ultimate and the laptop has xp sp2.

Anyone bored on a Sat night who can help??

Mart