AJAX Modal Popup

Hi I hope someone can help, but this is driving me nuts!

At the moment I'm just trying to create a simple Modal popup and I've tried lots of things and spent ages looking at examples. However, I just can't get one to work!

My Code:

<div id="Options"><asp:ImageButton ID="OptionsImgBtn" runat="server" ImageUrl="../Images/Options.png" AlternateText="Options"/><asp:ModalPopupExtender ID="MPE" runat="server" TargetControlID="OptionsImgBtn" PopupControlID="OptionsPanel" DropShadow="true" /><asp:Panel runat="server" ID="OptionsPanel">
        Options Panel</asp:Panel></div>

Thanks for any help.