var win = null; 
function  abreAvisolegal(u){ 
  if (screen.width+"x"+screen.height == "800x600"){
	w=750; h=400; l=0; t=50;
  }else{
	w=800; h=450; l=50; t=50;
  }
  settings ='height='+h+',width='+w+',top='+t+',left='+l+',scrollbars=yes,resizable=no' 
  win = window.open(u,'aviso',settings);
  win.focus();
  win.moveTo(l,t);
}