function centeredPopup(page,name,w,h,features)
{
    var winl = 0;
    var wint = 0;
    if (screen.width) {
        winl = (screen.width-w)/2;
        wint = (screen.height-h)/2;
    }
    if (winl < 0) winl = 0;
    if (wint < 0) wint = 0;

    var settings = 'height=' + h + ',';
        settings += 'width=' + w + ',';
        settings += 'top=0,';
        settings += 'left=0,';
        settings += features;
    win = window.open(page,name,settings);
    win.window.focus();
}
function roll_over(img_name, img_src)
{
	document[img_name].src = img_src;
}