function opwin(Url)
{
// Url 
// widht
// height 
// scrollbar 0 yes 1 no 
// resize 0 true 1 false
width=400,height=300,scrollbar=1,resizable=1
ow = width;
oh = height;
os = scrollbar;
or = resizable;
var xposition=0; 
var yposition=0;
if ((parseInt(navigator.appVersion) >= 4 ))
  {
    xposition = (screen.width - width) / 2;
    yposition = (screen.height - height-25) / 2;
  }
  window.open (Url,"","width ="+ow+",height="+oh+",scrollbars = "+os+",resizable="+or+",left="+xposition+",top="+yposition );
}