Ajax enabled radio button and others

I have two radio buttons radiobutton1 and radiobutton2 and two dropdownlist. dropdownlist1 and dropdownlist2.
What I want is that on page load both to be visible false no problem done that.
then on clicking radiobutton1 only dropdownlist1 appears and clicking radiobutton2 dropdownlist1 dissapers and dropdownlist2 appears. But I am putting this around
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
            <ContentTemplate>
            </ContentTemplate>
</asp:UpdatePanel>

So that it doesnt postback the whole page but putting update panel doesnt work.

How is this possible to make it work?

Please help.

Any help is much appreciated in advance

Thanks,

R8VI