Here is an ex.
on the link here you can see the content is in yellow and gray rounded box. And the bg image of the rounded table is only this for the bottom and this for the top. It is very clever and I would like to know how to do that.
Thank you !

There are many, many methods:
http://www.smileycat.com/miaow/archives/000044.php

Thanks for the list. I've seen quite a few of those methods, but not all and not all in one place. I also have a new design blog in my feed reader.

I have been using more and more mootools and jquery add on's

Here is a cool mootool rounded corner plugin.

http://www.phatfusion.net/roundedcorners/