try like this..
<asp:templatefield headertext="Comments" xmlns:asp="#unknown">
<asp:label id="lblComments" visible="<%# !Eval("IsInEditMode") %>" runat="server" text="<%# Bind("Comments") %>"></asp:label>
<asp:textbox id="txtComments" visible="<%# Eval("IsInEditMode") %>" runat="server"></asp:textbox>
</asp:templatefield>
hope it works..