I have had a frequent problem with the modem trying to disconnect from a server and getting hung up with a message "disconnecting" and it never finishes. Quitting or force quitting brings it right back to the same place when Internet Connect is restarted. The only solution I could find was to restart the computer. But I just discovered that if you put the machine to sleep and then wake it up again, the modem is disconnected so you can try dialing again.
[Editor's note: I don't know if the recent Networking system update will have any impact on this problem, which I have seen reported elsewhere.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020624100019876