According to the CSS Compatibility report for Microsoft Internet Explorer browser version 5 to 8 published
here, Microsoft doesn't intend to support the border-radius attribute of CSS 3 anytime soon - both Internet Explorer 8 Beta 1 and Internet Explorer 8 RTM will not have support for the property that can save us all from having to download tiny images of curves (not *that* kind of curves!) to view rounded borders.
Firefox supports the border radius, although it needs the "-moz-" prefix.