prueba esto, lo pude ver en este sitio
http://www.ezwp.com/
saludos
<head>
<script type="text/javascript">
function hideLoading()
{
document.getElementById('pageIsLoading').style.dis play='none'; // DOM3 (IE5, NS6) only
}
</script>
</head>
<body>
<div id="pageIsLoading" style="border-right: #999999 1px solid; padding-right: 12px; background-position: 6px center; border-top: #999999 1px solid; display: none; padding-left: 12px; font-weight: bold; background-image: url(Images/antes-2headerBg.gif); border-left: #999999 1px solid; width: auto; color: #000000; line-height: 40px; border-bottom: #890000 1px solid; position: absolute; height: 40px;">
<script type="text/javascript">
if (typeof window_width == 'undefined' || typeof window_height == 'undefined') {
var window_width;
var window_height;
if( typeof( window.innerWidth ) == 'number' ) {
window_width = window.innerWidth;
window_height = window.innerHeight;
} else if( document.documentElement &&
( document.documentElement.clientWidth || document.documentElement.clientHeight ) ) {
window_width = document.documentElement.clientWidth;
window_height = document.documentElement.clientHeight;
} else if( document.body && ( document.body.clientWidth || document.body.clientHeight ) ) {
window_width = document.body.clientWidth;
window_height = document.body.clientHeight;
}
}
var left = Math.round((window_width - 300) / 2);
var top = Math.round(((window_height - 46) / 3) + 46);
document.getElementById('pageIsLoading').style.lef t = left+'px';
document.getElementById('pageIsLoading').style.top = top+'px';
</script>
<img src="espere.gif" class="alineartextloadig">Cargando... Espere, por favor...
</div>
<div id="overDiv" style="position:absolute; visibility:hidden; z-index:1000;"></div>
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aqui va todo tu contenido del sitio
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<script type="text/javascript">
if (window.addEventListener) {
window.addEventListener('load', hideLoading, false);
} else if (window.attachEvent) {
var r = window.attachEvent("onload", hideLoading);
} else {
hideLoading();
}
</script>
</body>