function centreer()
{  
	if( typeof( window.innerHeight ) == 'number' ) 
 	{
		//Non-IE
		windowheight = window.innerHeight;
		windowwidth = window.innerWidth;
  	}
	else if( document.documentElement &&  ( document.documentElement.clientWidth || document.documentElement.clientHeight ) ) 
	{
		//IE 6+ in 'standards compliant mode'
		windowheight = document.documentElement.clientHeight;
		windowwidth = document.documentElement.clientWidth;
	}
	else if( document.body && ( document.body.clientWidth || document.body.clientHeight ) ) 
	{
		//IE 4 compatible
		windowheight = document.body.clientHeight;
		windowwidth = document.body.clientWidth;
  	}
	
	halfwindowheight = windowheight/2;
	
	var wrapperheight = document.getElementById("wrapper").offsetHeight;
	halfwrapperheight = wrapperheight/2;

	// alert("-"+halfwrapperheight+"px");
	document.getElementById("wrapper").style.marginTop = "-"+halfwrapperheight+"px";

}