[jQuery] animate background-position??

[sspboyd]

Hi,
I've been trying several ways to animate the position of a background
image and I'm stuck.

This is the code I'm using:

$("#header").click(function(){
        var bkgPosX=Math.round(Math.random()*(-500));
        var bkgPosY=Math.round(Math.random()*(-200));

        $("#header").animate({style: 'background-position: bkgPosX
bkgPosY;'},'slow');
        });

Any help is much appreciated!
Steve