You can connect to Pegasus with any telnet program that allows you to connect to a specific port (4242) or with a more sophisticated MU* client. The address is:
The Java client is down for now.
If you are using the Chrome browser, you can connect with the ChroMUD Client
The MUD Clients and Servers FAQ at MUDConnector.org lists clients for a number of platforms. Most of the folks on Peg use TinyFugue (Unix/Linux/Windows/MacOS) or Pueblo (Windows).