Can't connect G4 Mac Mini, to new 2009 Mac Mini via AirPort

Well, I bought a new Mac Mini and wanted my kids to use the old one for general web surfing. The first day I hooked it up with the AirPort to the new one and everything was great, we were Home Sharing iTunes, sharing files, etc. The next day when I powered up, I could not establish a connection. My settings seem the same, and I had them both connected (kids were browsing the web etc.) once, so I figure it can be done, but now I'm lost. Help!