help on creating overlay

Hello, iwould like the overlay to appear when i click on the add button, but im not sure how, and inside the overlay will be two buttons, submit, to enter the data into db, the overlay will close when this is click and clear button, toclear the textboxes, but the overlay won't close when this happen. I have done the interface first without the overlay, but now i want to add the overlay, any ideas on how to begin?
<table id="textbox" class="box" runat="server" visible="false" > <tr> <td width="100">Name:</td> <td width="120"><asp:textbox id="name" runat="server" /></td> <td><asp:Label ID="Label1" CssClass="text" runat="server"/> <asp:RequiredFieldValidator ID="a" CssClass="text" runat="server" ControlToValidate="eventid" ValidationGroup="AddGroup" ErrorMessage="* Required!" /> </td> <td class="text" width="200"> </td> </tr> <tr> <td width="100 ...