How do I get a rectangle to stretch the entire length of the screen?

I have used SiteBuilder for a number of years and have a lot of experience with it.  I am currently in the process of a re-design of one of my sites and I want to do something I have been unable to do so far :P

I want a rectangle or banner to go across the ENTIRE screen.  NOT just the length of my site width.  As an example, please visit www.wearecentralpa.com.  The pic banner is the length of the screen, not just the site.  If anyone has any information on how I can accomplish this, I would greatly appreciate the input.  I have tried extending the width of my site, and adding the rectangle, it still doesn't accomplish what I want.  Thanks!