onselectedindexchanged on Radios

[Angela]

Hi

I have populated a radio list from the database and I have dynamically
added another radio listitem which is <asp:listitem text="Use HO
Address" value="99"/>

I ONLY want the page to go off and call the sub GetHeadOfficeAddress
when the 'Use HO Address' item is selected. (It seems pointless to
submit the page when any of the other items are selected)

Currently I have a web control that looks like this

<asp:radiobuttonlist onselectedindexchanged ="GetHeadOfficeAddress"
autopostback="True" ....

Is there javascript that can be written to prevent the postback
happening when any of the other items are selected?

Or is there a better way of generating the radio list, so that there is
a onclick attribute on that particular 'Use HO Address' item

Thanks in advance,
Angela