var positiony=0;
$(document).ready(function(){
     $('.menu_principal h2 a.actif')
        .css( {backgroundPosition: "0px -233px"} )
        .mouseover(function(){
            $(this).stop().animate({backgroundPosition:"(0px 0px)"}, {duration:700})
        })
        .mouseout(function(){
            $(this).stop().animate({backgroundPosition:"(0px -233px)"}, {duration:700, complete:function(){
                $(this).css({backgroundPosition: "0px -233px"})
            }})
        })
});