Netscape 3.*:

From the Listening Post main page, click on the hypertext link of a server name. The Netscape news reader will open and a connection to the server will be made. Once the connection is established, use "Add Newsgroup" under "File" at the top menu. Don't forget to subscribe to by clicking the little dot just to the right of the newsgroup name. A check mark will appear.
 Repeat the process for each of the other listed servers.

Fort'e Agent/Free Agent:

Fort'e has a FAQ that includes instructions for using multiple news servers.

Microsoft Outlook Express:

Coming soon ...