The easiest thing to do is putting a div with the following CSS in the body:

#hideAll

 {

   position: fixed;

   left: 0px; 

   right: 0px; 

   top: 0px; 

   bottom: 0px; 

   background-color: white;

   z-index: 99; /* Higher than anything else in the document */



 }

(Note that position: fixed won't work in IE6 - I know of no sure-fire way of doing this in that browser)

Add the DIV like so (directly after the opening body tag):

<div style=display: none id=hideAll>&nbsp;</div>

show the DIV directly after :

 <script type=text/javascript>

   document.getElementById(hideAll).style.display = block;

 </script> 

and hide it onload:

 window.onload = function() 

  { document.getElementById(hideAll).style.display = none; }

or using jQuery

 $(window).load(function() {  document.getElementById(hideAll).style.display = none; });

this approach has the advantage that it will also work for clients who have JavaScript turned off. It shouldn't cause any flickering or other side-effects, but not having tested it, I can't entirely guarantee it for every browser out there.