How to install MediaWiki (via Fantastico) ?
Mediawiki is not included in the Fantastico automated installation tool. That is why its installation is relatively more complicated than those of Mambo or phpBB for instance.
Mediawiki can be downloaded from here: http://www.mediawiki.org/wiki/Download
Once you have downloaded the release you want, you can upload it to your account using the File Manager tool or via FTP. Click here to learn how to use FTP client, how to upload files using FTP and how to create FTP accounts.
In order to install Mediawiki with the File Manager, please, log into your cPanel from your Customer area, find File Manager icon and unpack Mediawiki file from your local hard drive into the desired folder.

Please, find below the instructions on how to perform the installation, once you have the files uploaded on your account:
Create a new database from the cPanel – MySQL Databases Area.
Add a username from the cPanel – MySQL Databases Area and add it to the database.
Open www.yourdomain.com/MediawikiDirectory/ (or without MediawikiDirectory if you have unpacked the files directly in the public_html folder) and press 'setup wiki'.
Fill in the following information: