I want to type www.aaa.com into url and then have a greasemonkey script that will load www.aaa.com but also load www.bbb.com right below www.aaa.com. You should be able to define the url for www.bbb.com.
my conceptual code:
// ==UserScript==
// @name google-wired
// @namespace test
// @include www.google.com
// ==/UserScript==
var secondURL = 'http://www.wired.com';
document.body.appendChild(HTML of second URL)
The output would be google's splashpage right on top of wired's splash page.