%lt;script language="JavaScript">
<!--
function SetBackground() {
if (screen.width == 640) {
document.body.background = "images/640x480.gif"; }
else if (screen.width == 800) {
document.body.background = "images/800x600.gif";
}
else {
document.body.background = "images/1024x768.gif"
}
}

</script> <body onLoad="JavaScript:SetBackground()">
NOTE: The onLoad= MUST be in the body tag.