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. Including loads of divs and spans make for really messy markup.
Tell you what - try Google > "rounded corners" css. You'll be amazed that there are webpages with this very info available for free. ;)
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 divs or spans.