Some time ago, I located this javascript on the net.
I'm not sure where it originated from, and it may even be outdated...all I know is, it works ok for me! ;-)
<!-- SCRIPT FOR RESIZING BACKGROUND IMAGE -->
<SCRIPT LANGUAGE="JavaScript1.2">
NS4 = (document.layers);
IE4 = (document.all);
scaleWidth = true;
scaleHeight = true;
<!-- Your image URL in the line below -->
imSRC = "images/weather.jpg";
if (NS4) window.onload = setResize;
function setResize(){
setTimeout("window.onresize=reDo;",500);
}
function reDo(){
window.location.reload()
}
if (IE4) window.onresize = reDoIE;
function reDoIE(){
imBG.width = document.body.clientWidth;
imBG.height = document.body.clientHeight;
}
function makeIm() {
winWid = (NS4) ? innerWidth : document.body.clientWidth;
winHgt = (NS4) ? innerHeight : document.body.clientHeight;
imStr = "<DIV ID=elBGim"
+ " STYLE='position:absolute;left:0;top:0;z-index:-1'>"
+ "<IMG NAME='imBG' BORDER=0 SRC=" + imSRC;
if (scaleWidth) imStr += " WIDTH=" + winWid;
if (scaleHeight) imStr += " HEIGHT=" + winHgt;
imStr += "></DIV>";
document.write(imStr);
}
//-->
</SCRIPT>
</HEAD>
<BODY MARGINHEIGHT=0 MARGINWIDTH=0>
<SCRIPT LANGUAGE="JavaScript1.2">
<!--
makeIm();
//-->
</SCRIPT>
<!-- END BACKGROUND RESIZE SCRIPT -->