function SelectItem()
{
    //This function is being called everytime a new page is loaded into
    //the "body" frame. 
    var frame = frames["header"];
    if (frame.SelectItem)
        frame.SelectItem();
}

<frame src="body.aspx" name="body" onload="SelectItem()" ....></frame>

var g_lastItem = null;

function SelectRoot(evnt, sender)
{
    //We no longer select the item when the menu item is clicked.
    //Instead we remember the item and wait for the target frame
    //to finish loading, at which point SelectItem is called
    g_lastItem = sender.getItem();
}

function SelectItem()
{
    //This function is similar to the original SelectRoot function,
    //except for that it is called when the new page finishes
    //loading instead of when the menu item is clicked
    var parent = g_lastItem;
    if (!g_lastItem)
        return;
                
    while (parent.getLevel() != 0)
    {
        parent = parent.getParentItem();
    }

    //This is needed to "remind" the menu that it should "get
    //ready". Otherwise certain internal data are not initialied
    //until you move mouse over the menu
    parent.setDisabled(true);
    parent.setDisabled(false);

    //Now select the menu item
    parent.setSelected(true);
    alert('selected');
}