I use more or less the same position: fixed code with PHP and it does work. It could be the path from the css file which is different in your PHP page.
http://www.wickham43.net/backgroundf...hflexible.html
However, you don't need the html, body {height: 100%;} unless there is something else that you need it for.
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.