The page  viewer doesn't take web  part connections, but it would be
pretty simple to do what you ask with normal HTML. Instead of using a
page viewer, just edit in SharePoint Designer and add an iFrame with a
name property, then add a form with the target set to the iframe name,
the action to the base URL (everything before the ? in your example) and
a single text  form field named "section".

How abouttwo page  Viewer web  Parts/ One web part  displays a web page with a
form that submits to the page that is viewed in the other web part.

Web Part One: Please enter the Section that you want to view : And the
web page that gets posted to takes the value from the form and displays the
section.