You can use this tab to let WWW Server listen on other ports than port 80. You can also use it to make different server sockets at different IP addresses, so you can use virtual hosting.
On Windows 98, you can first define a port on a specifical address, and then define the same port on no specifical address to mean all other addresses. On Windows 2000, this does not work, as it will give an "Address already in use" error message.
When using the NT Service, changes to the port settings are taken over immediately. When using the standalone application, you should click the "Start Server" button to activate port changes.
More information about virtual hosting can be found at the Virtual Folders page.