I haven't quite figured out how to manually set it up on the Web Admin page. But the Orbiter seems to scan for devices constantly, so wait for it to pop up with "Device Discovered" and set the user name and password. That seems to be the easiest for me. I'm used a Lacie ethernet drive that's set up as a Windows Share device.
The Web Admin page isn't very intuitive, you have to know what your doing. I'm waiting for a LinuxMCE setup for idiots guide.