I've almost figured out how to do it. I've managed to move my Adsense ad to the top of each page See for example
http://www.countyhistorian.com/cecilweb/index.php/Current_events
But I think that Adsense has this Slot Id I have to tell it now, that the ad should be a banner, not a box. I think that's the remaining problem here.
W