A cool article which tells you about rounded coreners which will work in all the browsers including ie6!...

http://htmlcsstutorials.blogspot.com/2009/06/niffy-rounded-corners-using-html-and.html

i think that you can find out on http://www.roundedcornr.com/
i found that but i dont know if it works so try it out.

the CSS only works in Mozilla browsers (and flakey at that). You generally need to revert to a 9 image construct for variable width/height. Sometimes you can do it with 3 (top/bottom/mid images)

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Here's a site that makers the corners automatically for you and spits out the code to use.

http://www.spiffycorners.com/

A List Apart has some excellent ideas for using CSS. Here's one.

I know how to do it using graphics, but I would prefer to use code.