Changing a redirect depending on selection
You can add your own submit handler to your form. In the submit handler function you will be able to access the value that was entered by the user.

The code could look something like this (to be put in a custom module).

    /**
    * Implementation of hook_form_alter()
    */
    function MYMODULE_form_alter(&amp;$form, &amp;$form_state, $form_id) {
      if($form_id == 'MY_FORM') {
        // Adds our own custom submit handler to the form MY_FORM
        $form['#submit'][] = 'MYMODULE_MYFORM_custom_submit';
      }
    }

    /**
    * Custom submit handler for MY_FORM
    */
    function MYMODULE_MYFORM_custom_submit($form, &amp;$form_state) {
      $form_state['redirect'] = 'my-path';
      $form_state['rebuild'] = TRUE;
    }


Replace 'my-path' with the value the user entered. Look inside $form_state['values'] to find it. Don't forget to check that the value is valid so no funky stuff is done here :)

Good luck.