Network connection keeps dropping, but only when....

So I brought my wife's laptop to her parents and her father has a wireless-g set up. She can connect to it, but as soon as we start using the internet, the whole connection drops, for all the computers. Its like her computer is causing a problem with the router. It doesn't matter if she goes wireless or if I turn off her wireless and plug into the router. So its not really a wireless problem.
Anyone have any ideas? Its odd because her laptop causes no problems whatsoever on my network at home. And her sister's laptop doesnt cause much of a problem for her parents network.

Its the worst when we try to play a LAN game - then the connection will disconnect and reconnect constantly - like every 10-15 seconds. But If only one person is using the internet, it usually is stable.
But as soon as we try to all use it or play a LAN game, kaboom

Please, any suggestions would be great. Perhaps something with the router can be altered or maybe there is something on her laptop that is causing a screwup.