Auto complete on a checkbox list how to?

Hi,

I've Text box wich i fill from a checkboxlist, each item that is checked will be placed in the textbox (In this case every email adres will appear as acheck box)

The checkboxlist will apear in a ajax popupControlExtender (See code below)

Now i need a textbox with a autocomplete function to search true the checkboxlist for a specific email adress...Does anybody knows how to do this?

<script type="text/javascript">

        $(function () {
            $('#btn3').button({
                icons: { primary: "ui-icon-search" },
                text: false
            });
        });

    function CheckBoxListSelect(cbControl, state) {

        var chkBoxList = document.getElementById(cbControl);

        var chkBoxCount = chkBoxList.getElementsByTagName("input");

        for (var i = 0; i < chkBoxCount.length; i++) {
            chkBoxCount[i].checked = state;
        }
        return false;
    }</script><form id="form1" runat="server"><div><asp:ToolkitScriptManager runat="server"></asp:ToolkitScriptManager><asp:UpdatePanel ID="updatepanel1" runat="server"><ContentTemplate><asp:TextBox ID="TextBox1" runat="server" TextMode="MultiLine" Rows="10" Width="250px"></asp:TextBox><br /><button id="btn3" runat="server"></button><asp:PopupControlExtender ID="TextBox1_PopupControlExtender" runat="server" DynamicServicePath=""
                    Enabled="True" ExtenderControlID="" TargetControlID="btn3" PopupControlID="Panel1"
                    OffsetY="22"></asp:PopupControlExtender><asp:Panel ID="Panel1" runat="server" CssClass="ui-widget-content"
                    Direction="LeftToRight" ScrollBars="Auto"
                    Style="display: none;">
                    Select <a id="A1" href="#" onclick="javascript: CheckBoxListSelect ('<%= CheckBoxList1.ClientID %>',true)">All</a>
|                          <a id="A2" href="#" onclick="javascript: CheckBoxListSelect ('<%= CheckBoxList1.ClientID %>',false)">None</a><br /><asp:TextBox ID="txtSearch" runat="server" /><asp:CheckBoxList ID="CheckBoxList1" runat="server" DataSourceID="SqlDataSource1"
                        DataTextField="LoweredEmail" DataValueField="LoweredEmail" AutoPostBack="false"
                        OnSelectedIndexChanged="CheckBoxList1_SelectedIndexChanged"></asp:CheckBoxList><asp:Button ID="btn4" runat="server" CssClass="button-icon-se" OnClick="btn4_Click" /><asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:conn %>"
                        SelectCommand="SELECT DISTINCT LoweredEmail FROM [Membership]"></asp:SqlDataSource><asp:AutoCompleteExtender ID="AutoCompleteExtender1" TargetControlID="txtSearch"
                        runat="server" ServiceMethod="GetCompletionList" UseContextKey="True" /></asp:Panel></ContentTemplate></asp:UpdatePanel></div></form>
C#:

    protected void btn4_Click(object sender, EventArgs e)
    {
        string name = "";
        for (int i = 0; i < CheckBoxList1.Items.Count; i++)
        {
            if (CheckBoxList1.Items[i].Selected)
            {
                name += CheckBoxList1.Items[i].Text + ";" + "\r\n";
            }
        }
        TextBox1.Text = name;
    }

Best regards,

Mark