call a function from clicking the enter key

Hello. While I thougth that this would be a very simple thing to add, I consistently get a   'No Overload' error no matter what I try.
I have an open source web project in c#. The common solution was to use images instead of buttons, and write an event that fires when the image is clicked.  I have 2 pages that I am trying to call the image click event, but I can't get either to work.
Page 1 HTML: 
<asp:TextBox id="Loginpassword" TextMode="Password" maxlength="100" Columns="42" runat="server" /> <input id='LoginButton_DoLogin' type="image" border="0" src='<%#"Styles/" + PageStyleName + "/Images/" + Resources.strings.CCS_LanguageID + "/ButtonLogin.gif"%>' value="<%#Resources.strings.CCS_LoginBtn%>" OnServerClick='Login_Button_DoLogin_OnClick' ...