-- Wireless Router: - The buffalo is/was one of the first wireles routers to support the new 802.11g support. It also supports a variety of security methods, including WPA and RADIUS authentication. You can also vary the strength of the output of the base station, thus allowing you to "tune" you signal area (so you're not broadcasting further than you want to). Having said that 20m, even through good thick walls shouldn't present a problem - I've done more
You could even buy additional aerials for both base and card is signal strength becomes a problem (not that I think it would).
Its a very small unit, so placing next to your existing cable installation, then running the other PC's off the built in switch is simple enough to do.
Unforunately don't know enough about the wireless capabilities of the centrino range - think it's limited too 11mbps but don't know for certain.