TabContainer Setting Focus to a control inside the TabPanel

 Place this at the BOTTOM of your ASP.Net Page.  Replace txtPartNo with the name of your control.

<script language="javascript" type="text/javascript">
    Sys.Application.add_load
    (
        function()
        {
            window.setTimeout(focus, 1);
        }
    )
    function focus()
    {
        document.getElementById('<%=txtPartNo.ClientID %>').focus();
    }
</script>