I had a similar problem some time ago. The computer connected to the internet when an ethernet cable was used, but not wirelessly (!) Router is a Netgear DG834G ver.2. I found that carefully going through all the steps to install the computer solved the initial problem. I think that the computer had to be 'registered' with the router to be recognised. At least, that's my interpretation of events. I still suffer from low signal strength, which maybe due to a crowded internet neighbourhood ( at least 12 presently in my vicinity - who are you ' Horny Beast' ? ) or to distance from the router and brickwork or filing cabinet shielding. Hey Ho, back to the drawing board. All a bit academic, since the Q. is dated September 08, and I'm answering towards the back end of November ( still 08 though.)
Ian
November 2008