$("a.mnu_hover,a.menu_hover,a.hover").hover(
  function () {
    $(this).children("img").attr("src", function() { return this.src.replace( /\.(gif|jpg|jpeg|png)$/gi , '1.$1') } );
  },
  function () {
    $(this).children("img").attr("src", function() { return this.src.replace( /1\.(gif|jpg|jpeg|png)$/gi , '.$1') } );
  }
);

$("div.mnu_hover,div.menu_hover,div.hover,li.mnu_hover,li.menu_hover,li.hover,tr.mnu_hover,tr.menu_hover,tr.hover,td.mnu_hover,td.menu_hover,td.hover").hover(
  function () {
    $(this).css("background-image", function() { return this.src.replace( /\.(gif|jpg|jpeg|png)$/gi , '1.$1') } );
  },
  function () {
    $(this).css("background-image", function() { return this.src.replace( /1\.(gif|jpg|jpeg|png)$/gi , '.$1') } );
  }
);