function popup(winUrl,winName,winX,winY)
{
    var newWin;
    var randNum;
    if(!newWin||newWin.closed)
    {
        winTop=(screen.height-winY)/2;
        winLeft=(screen.width-winX)/2;
        randNum=Math.round(Math.random()*1000000);
        winRandName=winName+randNum;
        newWin=window.open(winUrl,winRandName,'width='+winX+',height='+winY+',top='+winTop+',left='+winLeft+',location=no,menubar=no,toolbar=no,status=no,resizable=no,scrollbars=yes');
    }
}