Can't connect iMac with AirPort card/base
 

I have an iMac connected to the internet via cable modem (ATT @home). I had no problem connecting with LimeWire when I connected my iMac to my cable modem with a direct ethernet cable connection. Now, I am connected to my cable modem via an AirPort card and base station (base station connected to cable modem by ethernet cable -- AirPort card in iMac), and I can't connect to the gnutela network. All of my other internet applications work fine. Has anyone out there seen this before?