Fluid Bootstrap 2.0 でスクロール時にサイドバーを固定する方法は?

.sidebar-nav-fixed {
    padding: 9px 0;
    position:fixed;
    left:20px;
    top:60px;
    width:250px;
}

.row-fluid > .span-fixed-sidebar {
    margin-left: 290px;
}

<div class="container-fluid">
  <div class="row-fluid">
    <div class="span3">
      <div class="well sidebar-nav sidebar-nav-fixed">
        ...
      </div>
    </div>
    <div class="span9">
      ...
    </div>
  </div>
</div>

@media (max-width: 767px) {
    .sidebar-nav-fixed {
        width:auto;
    }
}

@media (max-width: 979px) {
    .sidebar-nav-fixed {
        position:static;
        width: auto;
    }
}