SOLVED!!! Mac Mini Setup Keyboard Fix
I just purchased a Mac Mini Server 2009 from Gumtree.
Plugged it in to my screen and usb wireless mouse, only to get to the Administrator Account page where I had to type info.
I couldn't connect my wireless keyboard, but eventually did this.
1. Right click in the 'Name' section
2. Select Substitutions -> 'Show Substitutions'
3. Click 'Text Preferences'
4. Up the top left click 'Show All'
5. This opens up the main System Preferences screen where you can then go to 'Keyboard'
6. Connect your bluetooth keyboard!
I hope this helps save some time for someone who struggled like me!
Good luck!