Rounded corners can be achieved very simply in ever browser using a mix of CSS3 and JavaScript. Normally this is achieved in Internet Explorer using a mix of background images and CSS classes. CurvyCorners is a free JavaScript library for creating simple, yet beautiful rounded corners. The result looks like this:

The advantage to using this method is that it allows you to render rounded corners in Chrome, FireFox, and Safari using the CSS3 properties -webkit-border-radius and -moz-border-radius. While in Internet Explorer and Opera using the JavaScript alternative.