This CSS3 technique (border-radius) works fine for Mozilla/webkit browsers, but not IE (not even IE8 - as far as I know). IE requires a 'fallback' method which probably includes extra markup - be it...

Rounded corners can also be applied via JS, but you'd be better off looking at a pure css/html solution. Try, if possible, to keep the integrity of your html and not include too much 'design' markup....