<!--[if IE 7]><link rel="stylesheet" type="text/css" href="/css/IE7.css" /><![endif]-->  

.ie7blanklink
{
    display:inline-block;
}

<a title="Click Me" class="ie7blanklink" style="background: url('/images/email_trim.gif') no-repeat right center; padding-left: 20px; margin-left: 5px;" onclick="updatePermission(this);return false;" href="#" id="email_0"></a>

IE7 will not show background images on a item that has no text. This is probably true with ie6 as well. 

The best trick I've found is to display:inline-block, but you must do this for ie7 only

IE7 Background images on a blank link

HTML