Ethernet is a great way to talk to cameras that are hundreds of feet away from the computer. These are the options available:
SBIG sells an Ethernet to Parallel (E2P) adapter that allows you to connect your Parallel port based camera to Ethernet. This small box is all you need at the camera to talk Ethernet to your Parallel camera.
SBIG gives away for free Ethernet Server Software for Windows (EthSrvWin) that uses a Windows computer at the camera end of the connection to serve the USB and Parallel port cameras. You can download the software here.
Both these previously mentioned products are for connecting you cameras to a LAN, not to the Internet.
Software Bisque however sells an excellent package called CCD Remote that manages your entire Observatory over the Internet.