svn checkout -r29 https://zerowing.idsoftware.com/svn/radiant.gamepacks/Q3Pack/trunk/ ./GtkRadiant/games/Q3Pack
svn checkout https://zerowing.idsoftware.com/svn/radiant.gamepacks/UFOAIPack/branches/1.5/ ./GtkRadiant/games/UFOAIPack
For other game packs, see https://zerowing.idsoftware.com/svn/radiant.gamepacks/
svn checkout -r29 https://zerowing.idsoftware.com/svn/radiant.gamepacks/Q3Pack/trunk/ ./GtkRadiant/games/Q3Pack
svn checkout https://zerowing.idsoftware.com/svn/radiant.gamepacks/UFOAIPack/branches/1.5/ ./GtkRadiant/games/UFOAIPack
For other game packs, see https://zerowing.idsoftware.com/svn/radiant.gamepacks/
+ Note that they must be in GtkRadiant 1.5's format (like the ones in a branches/1.5 subfolder)!