function a(f, n, w, h) { 
  var lft = screen.width/2-320; 
  var tp = screen.height/2-240; 
  var d = 'width='+640+',height='+480+',top='+tp+',left='+lft; 
  window.open(f, n, d);
}

function b(f, n, w, h) {
  var d = 'width='+640+',height='+320+''; 
  window.open(f, n, d);
}