Background Image - Can we make it stretch?

...and by 'stretch' I mean automatically resize in width to the same size of the window. Say I'm making a course for a screen res of 1920 by 1080, but I know some users will have smaller monitors, so make the content area (IE all pages) about 1024, then i have the background centered and it changes to the size of the users current window width (whatever that may be).

I know someone has written a way to do it somewhere...hopefully those people could see this.

Is there some html that is compatible and works a charm?

If so I'm happy to put the answer in the 'tips and tricks' section.

Thanks in advance.

-casper.