var click_win = null;
function openWin(url) {
var linkUrl = url; 
var NS = (navigator.appName=="Netscape")?true:false; 
w = 720; 
h = 518; 
if ( ( click_win != null ) && (!click_win.closed ) )
{
   click_win.close ();
}
LeftPosition = (screen.width) ? (screen.width-w)/2 : 0;
TopPosition = (screen.height) ? (screen.height-h)/2 : 0;
sAttr = 'resizable=0,scrollbars=0,toolbar=0,location=0,status=0,height='+h+',width='+w+',top='+TopPosition+',left='+LeftPosition  
click_win = window.open( url, "", sAttr); 

}