Check all machines and the router for firewall settings.
I have a DLink DIR-655 router with the latest firmware that is about a month old. I have 2 wired connections to PC's and one new Hypersonic laptop that has built in N wireless card. None of the 3 computers have a problem with getting to the internet, and I can share files between them with no problem. The problem is we like to play 3 way games across the LAN. Any game we try (Age of Empires 3, Far Cry, etc.) with a wireless connection, we cannot see the other computers to join the game. If I plug in the wired connection, it works fine. Any help would be very much appreciated.