Hr Tag in IE - remove border
See http://webdesign.about.com/od/beginningcss/a/style_hr_tag.htm
It seems that there is no good way around this problem, only with a hack (using a surrounding div).
To avoid these problems, you could use DIV tags instead. In order to make it accessible, put an HR inside like this:
<div class="ruler"><hr /></div>
then apply styles to it:
.ruler { border-top: 1px solid black; }
.ruler hr { display: none; }
This will hide the HR and make the DIV a "horizontal ruler".