I'm not entirely sure what you want to do here. If you could give us a little bit more info, I am sure someone would be happy to help you? Are you trying to get rid of tables in your layout?
Can be done with the "border-radius" propertie of CSS3, however CSS 3 is not widely supported by current browsers. Anyway take a look at this page to show old and new techniques: Rounded Corners with CSS and JavaScript.
do check out tutorialblog.org which features loads of generators that you can use to round images and things and lots of nifty such stuffs..