The web server allows you, when the unit is connected to a network, type in the IP address in a web browser and 'see' it. You don't program it that way though. The 1100's come with DHCP enabled which means if you connect it to a network there has to be a DHCP server out there somewhere to give it an IP address. If not, which is typical in a home network, you wont be able to communicate via ethernet. However, if you go online with it via the serial port (RsLogix 500) you can give it a static IP address (and disable DHCP and BOOTP) and then connect via the ethernet port. Communicating via ethernet is much faster so that is what I typically do.
If you have the Rockwell BOOTP server program you can use that to set the IP address directly without using the serial port, then you don't even need a DF1 cable.