If you need to add a checkbox in your gridview, do the ff:
<asp:templatefield itemstyle-width="10px" xmlns:asp="#unknown">
<HeaderTemplate>
<asp:checkbox id="chkAllItem" runat="server" />
</HeaderTemplate>
<itemtemplate>
<asp:checkbox runat="server" id="chkItem" />
</itemtemplate>
<itemstyle width="10px" />
</asp:templatefield>
If this doesn't answer your question, please let me know.
Regards,
Eduard