[jQuery] Trouble with backgroundPosition Plugin

[rob]

Having some trouble with this plugin.  I've tried in both IE8 and FF3,
but it doesn't seem to work.

Basically the background position isn't moving...

the function toArray(strg) is suppose to return the following....

return [parseFloat(res[1],10),res[2],parseFloat(res[3],10),res[4]];

this is the line where I'm getting an error code.  The values res[2]
and res[4] are coming back as NaN.  I'm not sure what these values
represent, or why they are Null.

I'm calling the backgroundPosition like this:

                        $('#nav li')
                                .css({backgroundPosition: "-150px 0px"})
                                .mouseover(function(){
                                        $(this).stop().animate(
                                                {backgroundPosition: "300px 
0px" },
                                                {duration:200})
                                        });


my css reads:

#nav li {
        background:url(../gfx/btn_navbg.jpg) 0px 0px;

        float:right;
        min-width: 100px;
        max-width: 150px;
        margin:0;
        padding:0;
        text-align:center;
        }


Any help would be much appreciated.