Dot Net Code Snippets

Hi i have came across one task, ie: I have dropdownlist that has some items along with 'Others' So if the user Choose the value Others -  i have to visible the Textbox and Validator so user should enter somthing on the textbox else it show Validation error if the user choose any other item , i have to disable the Textbox and the Validator.

Using Javascript its easy to do this , i am not good in Javascript i got a help from the Expert to make it work.

ASPX

<asp:DropDownList ID="EducationLevel_DropDownList" runat="server" Width="202px"
                                            Font-Names="Verdana" Font-Size="10pt" AppendDataBoundItems="True">
                                            <asp:ListItem Value="-1">Select</asp:ListItem>
                                            <asp:ListItem Value="1">PhD</asp:ListItem>
                                            <asp:ListItem Value="2">PhD Student</asp:ListItem>
                                            <asp:ListItem Value="3">Master Degree</asp:ListItem>
                                            <asp:ListItem Value="4">Bachelor Degree</asp:ListItem>
                                            <asp:ListItem Value="5">Under Graduate Student</asp:ListItem>
                                            <asp:ListItem Value="6">Others</asp:ListItem>
                                        </asp:DropDownList>
                                        <asp:RequiredFieldValidator ID="RequiredFieldValidator5" runat="server" ControlToValidate="EducationLevel_DropDownList"
                                            Display="Dynamic" ErrorMessage="Education Leve required !" InitialValue="-1"
                                            SetFocusOnError="True" ValidationGroup="Profile" Font-Size="8pt">*</asp:RequiredFieldValidator><asp:TextBox ID="TextBox1"
                                                runat="server"></asp:TextBox> <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="TextBox1"
                                            Display="Dynamic" ErrorMessage="Education Leve required !" 
                                            SetFocusOnError="True" ValidationGroup="Profile" Font-Size="8pt">*</asp:RequiredFieldValidator>

<asp:DataList ID="DataList1" runat="server" RepeatColumns="5" CellPadding="5">
            <ItemTemplate>
            <asp:Image Width="100" ID="Image1" ImageUrl='<%# Bind("Name", "~/images/{0}") %>' runat="server" />
                <br />
                <asp:HyperLink ID="HyperLink1" Text='<%# Bind("Name") %>' NavigateUrl='<%# Bind("Name", "~/images/{0}") %>' runat="server"/>
            </ItemTemplate>
                <ItemStyle BorderColor="Silver" BorderStyle="Dotted" BorderWidth="1px" HorizontalAlign="Center"
                    VerticalAlign="Bottom" />
</asp:DataList> 

protected void Page_Load(object sender, EventArgs e)
    {
        ListImages();
    }

    private void ListImages()
    {
        DirectoryInfo dir = new DirectoryInfo(MapPath("~/images"));
        FileInfo[] file = dir.GetFiles();
        ArrayList list = new ArrayList();
        foreach (FileInfo file2 in file)
        {
            if (file2.Extension == ".jpg" || file2.Extension == ".jpeg" || file2.Extension == ".gif")
            {
                list.Add(file2);
            }
        }
        DataList1.DataSource = list;
        DataList1.DataBind();
    }