In CSS3, border-radius is the rule you would use to achieve curved corner borderlines, but for now, IE and Opera doesn’t support this trick. With a little script help in the form of a .htc, you can make a cross browser compatible rounded corner box such as a <div> or an <img>.
-moz-border-radius: 9px; -webkit-border-radius: 9px; border-radius: 9px;
The above CSS rules set bends all 4 corners of any box, but only in FF, Chrome and Safari. To make it work in IE, you have to refer to this trick by Remiz.