interestingly the subversion build of gtkradiant seems to have a different folder setup when it comes to the games you map for.
the old version would have lots of game related folders like oa.game, q1,game, q2.game, q3.game etc... and then in the games folder there would be files like oa.game etc.
the new version doesn't have any of the old q3.game type folders. instead, everything is in the gamepack which is in the games directory. i downloaded the quake3 gamepack with...
svn checkout
https://zerowing.idsoftware.com/svn/radiant.gamepacks/Q3Pack/trunk/ Q3Pack
... and had a look at it. i'm not really sure how to change it for openarena. anyone done it yet?