Items 17, 18 and 19 here
http://www.wickham43.net/firefoxbackground.php
show different methods.
If you have a containing div with a fixed width, the background image method in item 18 is fairly easy. The other methods involve complicated nesting of divs or extra divs with position: absolute behind the divs with content.
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.