I have some css that specifies an image as the background for the page body

body 
{
	background-image: url(../images/EBSMainBackground.jpg);
	background-repeat: no-repeat;
	background-position: left bottom;
	font-family: Trebuchet MS;
	font-size: 12px;
	background-attachment: scroll;
}

this works fine until I maximise the width of my web page and the image cuts off horizontally (obviously the width of the image is less than the full page width)

Is there a way with CSS that will stretch the background image so that it will always fit the whole page width no matter what size ?

No, currently that is not supported:

http://www.webmasterworld.com/forum83/303.htm
http://webdesign.about.com/od/css3/f/blfaqbgsize.htm

Hopefully it will be supported with CSS 3.

There is a trick most web designers use:

Repeat-x css property. That way your small image will cover the entire area along the x axis (horizontally).

For eg take a look at this website. http://tonyyoo.com/v2/

If you have a large monitor ~ 22". The background image will seem to be a large one, but infact its 428px × 546px. The image just repeats itself along the x axis.

This trick works when the background image has a symmetry.

This website uses a 1px width image for the background. http://www.awarespot.com/