function resize_mainframe(){
	var breite =  (document.body.offsetWidth-1000)/2;
	var hoehe =  10 //(document.body.offsetHeight-500)/2;
	if ( breite > 0){
		with ( document.getElementById( "mainframe" ) ) {
			style.left=breite+"px";
		}	
	}
	
	if ( hoehe > 0){
		with ( document.getElementById( "mainframe" ) ) {
			style.top=hoehe+"px";
		}	
	}
with ( document.getElementById( "mainframe" ) ) {
			style.visibility="visible";
		}

}