1. First, make sure that all browsers have a 100% height, 0 margin, and 0 padding on the html and body tags:

          

   2. Add the image you want as the background as the first element of the Web page, and give it the id of bg:

          
          
          

   3. Position the background image so that it's fixed at the top left and is 100% wide and 100% in height. Add this to your style sheet:

          img#bg {
          position:fixed;
          top:0;
          left:0;
          width:100%;
          height:100%;
          }

   4. Add all your content to the page inside of a division called "content". Add this below the image:

          
All your content here - including headers, paragraphs, etc.

      Note: it's interesting to look at your page now. The image should display stretched out, but your content is completely missing. Why? Because the background image is 100% in height, and the content division is after the image in the flow of the document - most browsers won't display it.
   5. Position your content so that it's relative and has a z-index of 1. This will bring it above the background image in standards-compliant browsers. Add this to your style sheet:

          #content {
          position:relative;
          z-index:1;
          }

   6. But you're not done. Internet Explorer 6 isn't standards compliant and still has some problems. There are many ways to hide the CSS from every browser but IE 6, but the easiest (and least dangerous) is to use conditional comments. Put the following after your style sheet:

          ...
          
          

   7. Inside the comment, add another style sheet with some styles to get IE 6 to play nice: