Many people use an image for the curved bits, say an image only 5 or 10px high the full width of your rectangle with rounded corners and this sits on top of your rectangle.
You can turn the image upside down and put it below the rectangle for curved bottom corners.
Or make very small rounded corners say 10 x 10px curved in one corner which sit in each corner of your rectangle.
There are also javascript codes to make curved corners without needing separate images.
See
http://www.wickham43.supanet.com/tut...roundedcorners
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.