function av(u, an, al)
{

 var w=screen.width; 
 var h=screen.height; 
 var xx = an;
 var yy = al;
 var x = (w/2) - (xx/2); 
 var y = (h/2) - (yy/2);
	v = window.open(u,'ventana','resizable=0,toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=0,width='+xx+',height='+yy+',screenX='+x+',screenY='+y+',left='+x+',top='+y+'');		
	v.focus ();
}	




function av800x600(p) 
 {
  y = open(p,"",
    "scrollbars=yes,toolbar=yes,directories=yes,menubar=yes,resizable=yes,location=yes,directories=yes,status=yes,width=800,height=600"); 
 }