http://www.askthecssguy.com/2008/03/one_pixel_notched_corners_as_u.html
This time with two neseted elements with simple margin and border width declarations. (I had done this before I red the first comment :] )
Not tested in IE6.
.softener-outer {
border-width: 0.3em 0;
margin: 0 0.3em;
}
.softener-inner {
border-width: 0 0.3em;
margin: 0 -0.3em;
}