I was reluctant to post this, but I just thought, "Aww what the hell!" I've got my new Powerbook 5300c, and I bought it with a Global Village Powerport Platinum PC card that has ethernet and a modem. I have installed the driver software for it. I can get the modem to work, but the ethernet does not do anything. I think it's because appletalk won't recognize that there are other ports besides modem/printer and infared. There is an alternate ethernet option, but it says that nothing is connected. I have system 7.5.3 if that has to do with anything. Has anyone else had (or fixed) a similar problem?
Try moving up to 7.6 or, better yet, 8.1.