CSS Random Background Image

I have a website ready to go but need some Javascript/CSS tweaks. I have a background image div in CSS but want two scripts. - One script which will face background-image element between 5 JPEGS. - One script that will randomize the jpegs visible on each page. Code is: #header { width:999px; padding: 0px 0px 0px 0px; height:380px; /*background:url(images/[login to view URL]) left top no-repeat;*/ } Dont know enough about CSS to get it working. It needs to be done as CSS level as its a mod to all pages. Page code is... <div id="header"> <?php include("[login to view URL]"); ?> </div>