When you click on a link such as this
send me an e-mail (obviously a fake address), it will always default to opening your Mail client on your local machine. In this case, you have Mail set up to be the default e-mail client.
Since Adelphia doesn't provide an e-mail client other than their web-based one, you'll have to use either Entourage, Mail, or Thunderbird (whichever you prefer). Then you can set that default e-mail client in Mail as I noted above.
To use one of these clients, you'll need to set up the initial settings within the client. I personally prefer Mail as my e-mail client. To do this under most clients, go to Preferences within the client, and add a new account. The setting is a POP3 account. Under the username, enter in everything before the @ sign in your e-mail address. Both the outgoing and incoming mail servers are
mail.adelphia.net. Then check to see that you can send and receive mail.
Here's a
userguide with more information. Page 6 is of particular interest.
If you need more help, let me know!
-Ryan