var win = null;
function Centrar(pagina,titulo,w,h,scrollu,resize){
LeftPosition = (screen.width) ? (screen.width-w)/2 : 0;
TopPosition = (screen.height) ? (screen.height-h)/2 : 0;
settings ='height='+h+',width='+w+',top='+TopPosition+',left='+LeftPosition+',scrollbars='+scrollu+',resizable='+resize+'';
win = window.open(pagina,titulo,settings)
}