function centre() {
ns4 = (document.layers)? true:false;
ie4 = (document.all)? true:false;
	if (ns4) {pag = document.pagL;}
	if (ie4) {pag = pagL.style;}
	
	if (ns4) {ampladaF = window.innerWidth; alcadaF = window.innerHeight;}
	if (ie4) {ampladaF = document.body.clientWidth; alcadaF = document.body.clientHeight;}
	
	formulaX = (ampladaF*400)/800;
	formulaY = (alcadaF*300)/600;
	numY = parseInt (formulaY-215);
	numX = parseInt (formulaX-395);
	pag.top = numY;
	pag.left = numX;
	if (ns4) {pag.visibility = "show";}
	if (ie4) {pag.visibility = "visible";}
}