ajax update panel

hi, I have a problem with ajax.net controls. I have a form with some field. When I click a button I validete client-side the fields and then, only if the validation is ok, the page post his data to the same page. It works fine. Now I need to add the updatecontrol (ajax.net) with the script manager. If i do this the page make the validation control and even if it is not ok the page post his data. Why?

thanks

This my be what you need.

http://weblogs.asp.net/lkempe/archive/2007/03/26/asp-net-ajax-and-asp-net-validators.aspx