I am using your plug-in in a project that uses CSS 'themes', so I did
not want to hard-code any radius settings or colors in the cornerz
Javascript. code  I also use 'outset' borders in some themes, so
wanted to handle these corners if possible.

These changes were too extensive to add to the cornerz plug-in, so I
created a function to do the calculations and then pass the data to
cornerz. Here is a quick summary of what this function handles that
cornerz currently does not:

 * finds the background color automatically
 * finds the border-width without a topBorder
 * finds the border-colors without a topBorder
 * handles inset/outset borders (barely adequate)
 * reads moz-border-radius rules from CSS

I'm providing this in case you find some parts of it useful for a
future update to cornerz, like the loop to find the bgColor or the
readRadius subroutine.

/*
 *  roundCorners
 *
 *  Add radiused-corners for browsers that don't support it natively -
primarily IE
 */
function roundCorners (defaultRadius) {
  // TODO: See if there are other browsers we should handle here, like
Opera
  if (!$.browser.msie || !$.fn.cornerz) return;

  var showDebug = false;

  $('.cornerz').each(function() {

    if (showDebug && this.tagName=='TD') {
      alert( 'this.backgroundColor = '+ $(this).css
('backgroundColor') );
      var selector = 'TD';
      if (this.id) selector += '#'+ this.ID;
      else selector += '.'+ this.className.split(' ')[0];
      alert( '$('+ selector +').backgroundColor = '+ $(selector).css
('backgroundColor') );
    }

    var
      $Elem    = $(this)
    ,  h_radius  = readRadius(this, defaultRadius) // returns hash
like: { tl: '8px', tr: '8px' }
    ;
    if (!h_radius) return true; // no radius specified, SKIP/CONTINUE

    var
      options    = { background: '#FFF' } // default
    ,  h_border  = { tl: 'Top', tr: 'Top', bl: 'Bottom', br:
'Bottom' }
    ,  $Parent    = $Elem // init loop var
    ,  bgCol    = ""  // init loop var
    ,  borderStyle      // loop var
    ;
    // find the background color - ascend all the way to BODY if
necessary
    while (!bgCol || bgCol=='transparent') {
      $Parent = $Parent.parents(':first');
      bgCol = $Parent.css('backgroundColor');
      if (!$Parent[0] || $Parent[0].tagName=='BODY') break;
    }
    if (bgCol && bgCol != 'transparent') options.background = bgCol;

    for (corner in h_radius) {
      // only doing 1-corner at a time!
      options.corners = corner;
      // get/set radius for this corner
      options.radius = parseInt(h_radius[corner]);
      if (!options.radius) continue; // SKIP corner - 0-radius

      // read the width for the specific border/edge we are doing
      options.borderWidth  = parseInt($Elem.css('border'+ h_border
[corner] +'Width'));

      // read the style for this border/edge
      borderStyle = $Elem.css('border'+ h_border[corner] +'Style');
      // outset & inset borders require special handling
      if (borderStyle=='outset' || borderStyle=='inset') {
        // TODO: these colors suit IE - but maybe not other browsers?
        // use a darker color for th bottom-right corner
        if (borderStyle=='outset')
          options.borderColor = (corner == 'br') ? '#5F5F5F' :
'#D6D6D6';
        else // inset
          options.borderColor = (corner == 'br') ? '#D6D6D6' :
'#5F5F5F';
      }
      else // NOT outset or inset - use normal borderColor
        options.borderColor  = $Elem.css('border'+ h_border[corner]
+'Color');

      // apply the corner-radius
      $Elem.cornerz( options );

      /* DEBUG
      if (showDebug) alert(
        $Elem[0].tagName + ($Elem[0].id ? '#'+$Elem[0].id : '.class="'+
$Elem[0].className+'"') +
        '\n\ncorners = '+  options.corners +
        '\nradius = '+    options.radius +
        '\nbackground = '+  options.background
      );
      */
    }
  });

  // TODO - handle generic UI corner classes

  function readRadius (elem, defaultRadius) {
    var
      $E    = $(elem)
    ,  radius  = {}
    ,  moz    = '-moz-border-radius'
    ,  r
    ;

    if (r = $E.css(moz))        radius.tl = radius.tr = radius.bl =
radius.br = r;
    if (r = $E.css(moz+'-topleft'))    radius.tl = r;
    if (r = $E.css(moz+'-topright'))  radius.tr = r;
    if (r = $E.css(moz+'-bottomleft'))  radius.bl = r;
    if (r = $E.css(moz+'-bottomright'))  radius.br = r;

    if (!radius.tl && !radius.tr && !radius.bl && !radius.br) {
      // DEBUG - notify if this element has no radius set in CSS
      if (showDebug) alert(
        'Element has no radius (-moz-border-radius[-xx]) specified:\n
\n'+
        elem.tagName + (elem.id ? '#'+elem.id : '.'+elem.className)
      );
      // use the defaultRadius if one was passed
      if (defaultRadius)
        radius.tl = radius.tr = radius.bl = radius.br = defaultRadius;
      else
        return null;
    }

    return radius;
  }