$(document).ready(function(){

    $(".ButtonImage input").hover(
        function(){HighlightButton($(this),true)},
        function(){HighlightButton($(this),false)}        
    );
});

function HighlightButton(element,hover){
   if (hover)
        element.attr({src: element.attr("src").replace("button.gif","button-hover.gif")});
    else
        element.attr({src: element.attr("src").replace("button-hover.gif","button.gif")});
}