A good start would be to try and identify what the traffic is that is being sent out. If it is a Windows OS installed on the laptop then you can try to use NetMon (Network Monitor) to capture the traffic. I personally like using Ethereal. Once you figure that out, there are probably a number of people here that can help you narrow down the problem.

You might be able to download a diagnostic tool from the vendor to help you verify that it is not a hardware issue. As a guess I would say that it could be link speed negotiation gone wild. Try to manually set you link speed on the adapter to prevent it from auto negotiating.

Best of luck to you,

Rich