How to get antialiased lines?

[Abe Gillespie]

I just can't get this to work.  Can someone give me a sample MapFile config?

Here's what I have:
...
  OUTPUTFORMAT
    NAME "png"
    DRIVER gd/png
    MIMETYPE image/png
    IMAGEMODE rgba
    EXTENSION png
    TRANSPARENT on
  END
...
  LAYER
    NAME "rivers"
    DATA "rivers"
    STATUS on
    TYPE line
    CLASS
      COLOR 153 179 204
      STYLE
        SYMBOL "rounded-line"
        ANTIALIAS true
      END
    END
  END
...
SYMBOL
  NAME "rounded-line"
  TYPE cartoline
  LINECAP round
  ANTIALIAS true
END

MapServer info:
MapServer version 4.8.3 OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG OUTPUT=WBMP
OUTPUT=PDF OUTPUT=SVG SUPPORTS=PROJ SUPPORTS=FREETYPE
SUPPORTS=WMS_SERVER SUPPORTS=WMS_CLIENT SUPPORTS=GEOS INPUT=EPPL7
INPUT=GDAL INPUT=SHAPEFILE

Thanks for any help.
-Abe