You can't make a background-image stretch to any window resolution so you have to use a normal image. You can do this by using position: absolute or position: fixed and make sure it is behind other content by using z-index: -1;
Here's an example using position: fixed;
http://www.wickham43.net/backgroundf...hflexible.html
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.