You will need a combinaton of javascript and CSS.
body {
background: #FFFFFF url(images/mybgimage.jpg) no-repeat;
background-position: Zpx 0px;
}
where Z variable is the correct offset to match the users resolution, which is avaiable in javascript via screen.width variable.
Or an easier approach would be to use the server side scripting language (PHP, ASP, etc) to write the appropriate offset to the CSS body tag.
There are other approaches, such as aligning a <div> to the right, and putting its background to your desired image, but this has mixed results...