how can i get Html control id on the code behind page of asp.net

<tr>
<td class="style5">
<asp:Label ID="Label6" runat="server" Text="Invoice for:" Font-Bold="True"></asp:Label>
</td>
<td class="style6">
<table style="width:100%;">
<tr>
<td class="style14" id="tdDiv1" >
<telerik:RadAjaxPanel ID="PanelDiv1" runat="server" height="17px" width="239px">
</telerik:RadAjaxPanel>
</td>
<td id="tdDivOther">
<telerik:RadAjaxPanel ID="PanelDivOthers" runat="server" height="16px"
width="703px">
</telerik:RadAjaxPanel>
</td>
</tr>
</table>
</td>
</tr>




now here i have to access the td with id=tdDiv1 and id=tdDivOther

i even tryd writting runat="server" abt it's not working still
so what should i do nw?