function openWin(url, windowFeatures, width, height) {
xpos = (screen.width - width) / 2;
ypos = (screen.height - height) / 2;
xposParamName = "left";
yposParamName = "top";
if(navigator.appName.indexOf('Netscape') > 0) {
    xposParamName = "screenX";
    xposParamName = "screenY";
}
widthParam  = "width=" + width;
heightParam = "height=" + height;
xposParam   = xposParamName + "=" + xpos;
yposParam   = yposParamName + "=" + ypos;
window.open(url, '_blank', windowFeatures + ',' + widthParam + ',' + heightParam + ',' + xposParam + ',' + yposParam);
}