Rounded Corners with an image

Hi,

first of all, english is not my main language, so sry for all mistakes.
i want to get rounded corners around my widget containers without the moz, khtml,... css-attributes. i will put a new div above and under the widget-container and give him this background-image http://yfrog.com/59obenbg (this image is only for above)
my question is, how can i add a div to realize this and where do i have to place it, so that the div is exactly above and under the widget-container so that i can give them my background-images with the rounded corners?