I want to install and use MediaWiki in my XAMPP installed Moodle, but how?
This is not that difficult. In the XAMPP installed Moodle the Server Root can lie, for example, in the C:/Server/Apache folder and Document Root lies in C:/Server/Moodle folder, both paths are generally the same. The installation of the MediaWiki can then occur in the Moodle folder. There are no special provisions for the different use of database engines, Moodle using ISAM and MediaWiki using InnoDB, that can all be taken care of by PHP and MySQL. To make it work properly though, you may want to consider using VHosts in Apache, segmenting the server.