I've used mediawiki...that's a piece of shit script...there's was no spam protection feature and my site was overran by robots...you're better off going without in my opinion...however, if I recall correctly, there's no stylesheet, I had to use inline styles... and you have to change the localsettings.php page:
http://www.mediawiki.org/wiki/Manual:LocalSettings.php
The newest version has skins to come with it, if you want to change them,
http://meta.wikimedia.org/wiki/Skins
I think they want this script to be as difficult as possible...best of luck...I know I wasn't helpful but I hate to see a brother hangin' with no response to a month old question...