pop up box question

<asp:Hyperlink ID="GamePlay" runat="server" NavigateUrl='<%# Eval("FileName", "games/gamePlay.aspx?filename={0}") %>' Text="&lt;img src='images/imgGame.jpg' alt='alternate text' border='0'/&gt;"/><asp:ModalPopupExtender ID="mp" runat="server" TargetControlID="GamePlay" PopupControlID="pnl"></asp:ModalPopupExtender><asp:Panel ID="pnl" runat="server" Height="200px" Width="200px" BorderStyle="Solid"
        BorderColor="Black" Style="display: none">
        WARNING : This game has been flagged. It may contain inappropriate content not appropriate for users under the age of 18.
        Do you wish to continue?<asp:TextBox ID="txtComment" runat="server" TextMode="MultiLine" Rows="3"></asp:TextBox><br /><asp:Button ID="btnClose" runat="server" Text="Close" /></asp:Panel>

Hi, i want an ok and cancel button for my warning message when a link is clicked. The ok message should mean the game carries on to the hyperlink target and cancel keeps them on the current page,

how can i change my code to do this?

thanks