problem with internet printing in Vista Ultimate

I am getting the following error when I do the
[URL="http://server_name/printers/"]http://server_name/printers/[/URL] command to try and use and connect using
internet printing.

403 - Forbidden: Access is denied.
You do not have permission to view this directory or page using the
credentials that you supplied.

Is there any idea of what it is, and how to correct it. I am trying to
connect using Firefox and from a Win 7 machine into the Vista Ultimate
machine.

Thank you