Let’s see if IE 8 & 9 honour this,
function transparent_top_bar_bg_ie(){ ?>
<!--[if gte IE 8]>
<style type="text/css" media="screen">
#top-bar {
background: none !important;
border-bottom:0;
margin-top: 0px;
position: absolute;
overflow: visible;
}
#top-bar, .top-bar-preview .top-bar {
background: none !important;
}
</style>
<![endif]-->
<?php
}
add_action( 'wp_head', 'transparent_top_bar_bg_ie' );