Audrey:
if you want to link an image to an arbitrary target (internal wiki page
or external URL), you can use the so-called imagelink extension
originally written by Brion
See
http://www.google.de/search?hl=de&q=mediawiki+imagelink.php&btnG=Su…
for current locations on the Web.
To clarify, I know how to assign the logo image in
localsettings.php
....