... on a Windows 2008 server.
N.B. Check file extensions are visible, and your test pages are really html / PHP, not secretly .html.txt!
1. Download MediaWiki, put in a folder in inetpub
2. Download php, follow steps here to install
2a. Run php-cgi.exe from the command line to see if you have the right VC++ installed; it will error if not. Download the correct version for your php (32 or 64 bit) and run installer.
3. Create a MySQL database, and a non-root username and password for it. (Authentication type: Standard, NOT SHA256.) Make sure the user has CREATE etc permissions. Check this has worked (if using workbench) by logging out and using the new username to log in.
3a. Un-comment out the line in php.ini for the extension php-mysqli.dll
3b. Copy libmysql.dll into Windows/System32 folder