SharePoint has changed TREMENDOUSLY since 2000.
We use both MediaWiki and SharePoint at my job. Each has its strengths and weaknesses. We
use the wiki for general knowledge and SharePoint for documents.
SharePoint is a much more complex product than MediaWiki however. Don't install it
unless you are prepared to hire an in-house SharePoint expert or two. Any PHP programmer
can learn to be a MediaWiki admin, given time, but SharePoint administration requires a
deep background (in SharePoint) to do well.
DanB