<div id="nav">
            <ul>
                <li>
                    <asp:HyperLink runat="server" NavigateUrl="~/admin/">Home</asp:HyperLink>
                </li>
                <li>
                    <asp:HyperLink runat="server" href="#">Orders</asp:HyperLink>
                    <ul>
                        <li>
                            <asp:HyperLink runat="server" NavigateUrl="~/admin/orders.aspx">Add Order</asp:HyperLink>
                            <asp:HyperLink runat="server" NavigateUrl="~/admin/listOrders.aspx">List Order</asp:HyperLink>
                        </li>
                    </ul>
                </li>
            </ul>
        </div>

NOW THE CSS

#nav
{
    font-family: arial, sans-serif;
    position: relative;
    width: 900px;
    height: 30px;
    font-size: 13px;
    color: #ffffff;
    float: left;
    top: 0px;
    left: 0px;
    margin-left: 20px;
}

#nav ul
{
    list-style-type: none;
    height: 30px;
}

#nav ul li
{
    float: left;
    position: relative;
}

#nav ul li a
{
    text-align: center;
    display: block;
    text-decoration: none;
    color: #ffffff;
    line-height: 30px;
    padding: 0px 10px 0px 10px;
}

#nav ul li a:hover, #nav ul li a:focus
{
    color: #333;
    background: #fff;
}

#nav ul li ul
{
    display: none;
}

#nav ul li:hover ul, #nav ul li:focus ul
{
    display: block;
    position: absolute;
}

#nav ul li:hover ul li, #nav ul li:focus ul li
{
   
}

#nav ul li:hover ul li a, #nav ul li:focus ul li a
{
    display: block;
    color: #ffffff;
    text-align: left;
    background: #333;    
    width: 130px;
}

#nav ul li:hover ul li a:hover, #nav ul li:focus ul li a:focus
{
    background: #111;
    color: #fff;
}

hope tat helps