actually very easy.
all you need is to edit phpinclude_start template and add something like:
PHP Code:
// ############## Headerimage and text rotating #########
switch(intval(time() / 2) % 3)
{
case 0:
$banner = 'img1.jpg';
break;
case 1:
$banner = 'img2.jpg';
break;
case 2:
$banner = 'img3.jpg';
break;
}
then just put $banner into the place of your img tag of the header