.selector-to-be-rounded { 
  -moz-border-radius:10px;
  -webkit-border-radius:10px;
  -khtml-border-radius:10px;
  border-radius:10px;
  behavior:url(border-radius.htc);
}

.curved { 
  -moz-border-radius:10px;
  -webkit-border-radius:10px;
  -khtml-border-radius:10px;
  border-radius:10px;
  behavior:url(border-radius.htc);
}

http://code.google.com/p/curved-corner/

note that for the corners to work in IE, you need to install the htc code from http://code.google.com/p/curved-corner/

.curved { 
  -moz-border-radius:10px; /* Firefox */ 
  -webkit-border-radius:10px; /* Safari and chrome */ 
  -khtml-border-radius:10px; /* Linux browsers */ 
  border-radius:10px; /* CSS3 */ 
  behavior:url(border-radius.htc);  /* make IE use properties of border-radius */
}

border-radius with IE support using htc behavior

css

CSS