var displayBg = function (dir) {
    if (dir == -1) {
        $("prevHover").setStyle ({"backgroundImage" : "url('/photoGallery/images/rollPrevious.gif')"});
    } else {
        $("nextHover").setStyle ({"backgroundImage" : "url('/photoGallery/images/rollNext.gif')"});
    }
} 

var hideBg = function (dir) {
    if (dir == -1) {
        $("prevHover").setStyle ({"backgroundImage" : ""});
    } else {
        $("nextHover").setStyle ({"backgroundImage" : ""});
    }
}