<< Actually, you are trying to share the connection, in a sense. The MAC address is unique to the network interface card. When you hook up the modem to the desktop, the ISP sees the MAC of the desktop NIC and all is well. When you switch to the laptop, the ISP sees a new NIC and cannot identify it. The result is no connection.
I think.
You'd need two IPs to have two machines connected. In the not very long run, a router is cheaper.
(Smarter people please weigh in here. I think I've got this right but don't want to confuse Kevster with wrong info.) >>
Sounds correct to me. If your cable company logs MAC addresses, it will only allow you to get on with the one that you first register with. Some will allow up to 3 or 4 MAC addresses, but some will only allow 1. That might be your case. If you get a router, there's something in there called MAC cloning, where you hook up your computer to the first port, and it will clone the MAC address of the NIC on your desktop. Then you should be able to share the connection between your laptop and your desktop. Hope this helps.