Note: GTK Radiant 1.6 changed its file format, meaning that the OA pack that allows the editor to show OpenArena in the list of available games without having to manually modify configuration files, works with NetRadiant 1.5 and GTK Radiant 1.5, but NOT with GTK Radiant 1.6. You can however use the updated BSPC tool that comes with GTK Radiant 1.6, to compile .AAS files.
You can add support for OA into GTKRadiant with the help of these files : http://openarena.ws/svn/tools/radiant1_5/
See these threads for general instructions :
Detailed articles :
- For Windows : Configure GTK Radiant under Windows, Configure GTK under Windows
- For GNU/Linux : Configure GTK Radiant under Linux