Damned Internet Explorer! Never works right..

[xblight]

   <?php if ($_SESSION['cart']->count_contents() != 0) { ?>
        <li><a href="<?php echo zen_href_link(FILENAME_SHOPPING_CART, '', 'NONSSL'); ?>"><?php echo HEADER_TITLE_CART_CONTENTS; ?></a></li>
        <li><a href="<?php echo zen_href_link(FILENAME_CHECKOUT_SHIPPING, '', 'SSL'); ?>"><?php echo HEADER_TITLE_CHECKOUT; ?></a></li>
        <?php }?>
        <?
        if (isset($_SESSION['customer_id']) and $_SESSION['customer_id'] != '1') {
echo "<li><input type=\"image\" src=\"http://xblight.com/store/music/music.gif\" onClick=\"window.open('http://xblight.com/store/music/index.php','XBLight Music Player','width=450,height=320,left=400,top=25,screenX=400,screenY=25')\"></li>";
}     else {
echo "<li><input type=\"image\" src=\"http://xblight.com/store/music/music.gif\" onClick=\"window.open('http://xblight.com/store/music/musicalerror.html','XBLight Music Player (No Access)','width=450,height=320,left=400,top=25,screenX=400,screenY=25')\"></li>";
}  
?>

Can someone explain to me why that code works in everything except for IE?
www.xblight.com (click music on the way top)
Works perfectly in firefox and chrome, but im thinkin maybe i missed something and thats why it wont work in iexplore.
alright thanks