Symptom
Some PPP servers require you connect via a terminal window when establishing the dial-up connection. In this case, you must select "Connect using a terminal window (command line)" in the PPP Options pane of System Preferences. In some cases, the terminal window may appear blank instead of showing the expected login prompt when you connect from a Mac OS X client.
Solution
This is resolved in Mac OS X 10.2 or later. For earlier versions, press the Return key when the blank terminal window appears. The login prompt appears, and you can continue the login process normally.