If you can use jQuery, you can try BgSwitcher plugin to switch the background-image with effects, it's very easy to use.
For example :
$('.bgSwitch').bgswitcher({
images: ["style/img/bg0.jpg","style/img/bg1.jpg","style/img/bg2.jpg"],
effect: "fade",
interval: 10000
});
And add your own effect, see adding an effect types