Validation Controls
Introduced Validation groups.Developers faced one important limitation when using the validation controls. Since an ASP.NET page can include only one server-side form, there was no way to present multiple forms that included validation on the same page. Submitting any form in a page would trigger validation of all of the forms in the page.
This problem is solved in the ASP.NET 2.0 framework with the introduction of validation groups. In the ASP.NET 2.0 framework, the form controls, the button controls, and the validation controls have been modified to support a new property named ValidationGroup. Form controls in separate validation groups are validated independently.
more details..
http://msdn.microsoft.com/asp.net/whidbey/default.aspx?pull=/library/en-us/dnvs05/html/valgroups.asp
