Please help. how to add this image at the beginning of the header (K2)

hello i ve a header image with curved style corners to make the theme look softer. (using K2 theme)

the header image:
https://img19.imageshack.us/img19/7912/ustn.gif here (note that the image is white so you can see it buy selecting all the page)

my header codes are looking like this at the moment:

#header {
	position: relative;
	height: 0;
	background: #3371A3;
	background-image:url(images/ust.gif);
	background-position: top right;
	}

could anyone tell how i should change the code to place this image on the top to make the theme have curved corners instead of sharp.

the image mentioned above is 900x15px and called ust.gif im trying to put it on the header of K2 and then i want the main menu at the top of this curved header.

i ll appreciate any of your help & suggestions, thank you.