IE 6 and IE 7 will not work properly with widths set to auto. If you chose to use auto widths, you will need to use conditional CSS to set a pixel measurement for IE 6 and 7:
<!--[if IE 7]>
<style type="text/css" media="all">
ul#cssmw > li > span > a {
width: 100px;
}
</style>
<![endif]-->
<!--[if IE 6]>
<style type="text/css" media="all">
ul#cssmw li span a {
width: 100px;
}
</style>
<![endif]-->