function abre(pagina,width,height){
 x = window.screen.width;
 y = window.screen.height;  
 var left = (x/2)-(width/2);
 var top = (y/2)-(height/2);
 janela=window.open(pagina,'Pagina', 'width='+width+', height='+height+', top='+top+', left='+left+', scrollbars=yes, status=no, toolbar=no, location=no, directories=no, menubar=no, resizable=no, fullscreen=no');
 janela.focus();
}