Custom code our site so the background changes depending on the user's desktop resolution...

We want the background of our site to be coded so it looks like our twitter page background ([login to view URL]) we want our images to be on either side of our page content on [login to view URL] the problem is: when a user has a different resolution, the image is sometimes pushed off the page.? We need a coder to somehow make the background always appear the same so we can be on either side of the page content and our page will look like our twitter background. Thanks.