<script language="javascript" type="text/javascript">
        function txtenddate_onfocus() {
            var txtenddate = $dp.$('<%=txtenddate.ClientID%>');
            return WdatePicker({ onpicked: function() { txtenddate.focus(); }, maxDate: '#F{$dp.$D(\'<%=txtenddate.ClientID%>\')}', dateFmt: 'yyyy-MM-dd HH:mm:ss' });
        }
        function txtbegubdate_onfocus() {
            return WdatePicker({ minDate: '#F{$dp.$D(\'<%=txtbegubdate.ClientID%>\')}', dateFmt: 'yyyy-MM-dd HH:mm:ss' });
        }
    </script>

<input id="txtbegubdate" runat="server" class="Wdate" type="text" onfocus="return txtenddate_onfocus();"
                />
            到
            <input id="txtenddate" runat="server" class="Wdate" type="text" onfocus="return txtbegubdate_onfocus();"
                />    

很多用法可以去

My97DatePicker 官网有相应示例