In reviewing the accordionbehavior.js file, I found an event that I want to handle in my page javascript.  I'm not sure of the systax to do this in javascript.

Specifically, I want to handle the onHeaderClick event prior to the accordionbehavior.js file handling it. 

Thanks in advance and please provide a snippit if possible.

You can utilize the selectedIndexChanging event, which is fired whenever a header is clicked.  Just add a handler for that event: 

        <asp:ScriptManager ID="ScriptManager1" runat="server" />
        <script type="text/javascript">
            function pageLoad() {
                var acc = $find('<%= Accordion1.ClientID %>_AccordionExtender');
                acc.add_selectedIndexChanging(ClickHandler);
            }
            function ClickHandler() {
                // Do whatever you want.
                alert('Something is happening!');
            }
        </script>
        <cc1:Accordion ID="Accordion1" ... >