SetFocusOnError property
One of the newer features in ASP.NET 2.0 which required more JavaScript code injection in the previous ASP.NET versions is to set focus on a certain server control on page load
this feature is now supported in ASP.NET 2.0 You can use the Page.SetFocus method to pass the ID of a control that should receive focus or you can call the Focus method on the control directly.
1: Page.SetFocus("ControlID");
Also you can set the DefaultFocus property of the Form element to the ID of a control that should receive focus when the page is first loaded
1: <form id="formMain" runat="server" defaultfocus="control1">
you can refer to the focus feature here http://quickstarts.asp.net/QuickStartv20/aspnet/doc/tipstricks/default.aspx#focusapi
This feature has a similar one for the validation controls you can use the validation control SetFocusOnError to whether focus is set to the control specified by the ControlToValidate property when validation fails.
1: <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" SetFocusOnError="true" Display="Dynamic">
2: </asp:RequiredFieldValidator>
3: