Preventing page refresh on selecting from dropdownlist

Place your all controls or place necessary controls which will cause page reload in an UPDATEPANEL from toolbox(Ajax Extension toolbar) and place a scriptManger in the design page this will prevent loading page again and again.....and your work is over now..!!!
Hope this will help you.

<asp:updatepanel id="UpdatePanel1" runat="server" xmlns:asp="#unknown">
<contenttemplate>
District:<asp:dropdownlist id="ddl_dist" runat="server" autopostback="True" height="21px" width="172px">
</asp:dropdownlist>
Taluq:<asp:dropdownlist id="ddl_tq" runat="server" autopostback="True" height="24px" width="174px">
</asp:dropdownlist>                    

Place:<asp:dropdownlist id="ddl_place" runat="server" autopostback="True" height="24px" width="173px">
</asp:dropdownlist>

Pincode:<asp:dropdownlist id="ddl_pin" runat="server" enabled="False" height="25px" width="171px">
</asp:dropdownlist>
</contenttemplate>
</asp:updatepanel>