Disclaimer screen when adding new content
One way to accomplish this would be to make a small custom module utilizing hook_form_alter().  Substitute "example" with your module name to implement.

example.module

/**
* Implementation of hook_form_alter()
* Add Disclaimer Message to Article Create Form
*/
function example_form_article_node_form_alter(&amp;$form, $form_state) {
  if (arg(1) == 'add') {
    drupal_set_message('Legal Disclaimer: By filling out this form you are agreeing.','warning');
  }
}


example.info

name = "Example module"
description = "Adds a disclaimer to node/add/article page."
package = Example
core = 7.x


Or if you want a popup, you could instead use drupal_add_js and a little Javascript

example.module

/**
* Implementation of hook_form_alter()
* Add Popup Disclaimer to Article Create Form
*/
function example_form_article_node_form_alter(&amp;$form, $form_state) {
  if (arg(1) == 'add') {
    drupal_add_js(drupal_get_path('module', 'example').'example.js');
  }
}


example.js

// if user agrees continue, else redirect
if (!window.confirm('Legal Disclaimer: Press OK if you agree.')) {
  window.location.href='http://example.com';
}


Of course this is all pretty simple and ugly.  One could combine both approaches and using CTools Modal or JQueryUI build a prettier dialog.  With JQueryUI you might do:

example.js

// if user agrees continue, else redirect using JQueryUI
// requires JQueryUI loaded (you can use [drupal_add_js()][5] for this too).
(function ($) { 
  $(document).ready( function() {
    $("&lt;div&gt;&lt;h3&gt;Legal Disclaimer&lt;/h3&gt;&lt;p&gt;Do you agree?&lt;/p&gt;&lt;/div&gt;").dialog({
      resizable: false,
      height:140,
      modal: true,
      buttons: {
        "I Agree": function() {
          $( this ).dialog( "close" );
        },
        "No Way": function() {
          $( this ).dialog( "close" );
          window.location.href='http://example.com';
        }
      }
    });
  });
});