In my experience (and many others' as well), MacRadiant 1.4 doesn't work. I have MacRadiant 1.5 working. I have X11 1.1.3. My problem was that when I tried to install X11 from Apple.com, it said it wasn't needed. If you get the install disc, you can find it in optional installs (or maybe it was additional installs, i can't remember). You have to open X11 BEFORE MacRadiant, or else it won't work. Also, you have to show package contents (control-click) on the MacRadiant 1.5 app, go to contents, resources, sw, radiant15, and put a copy of trem.game FOLDER anywhere in the radiant15 folder, as long as it's not in another folder. The trem.game folder should contain a copy of the trem.game FILE (which is used next, just duplicate it and put it in the trem.game FOLDER). Then open the games folder (conveniently located in the radiant15 folder) and put in the trem.game FILE. Your system may want to open it with Chess (for whatever reason), but open it with TextEdit instead. Where it says enginepath_macos="(some random path)", change that path to wherever you copy of Tremulous is. Mine is /Applications/Tremulous/Tremulous (the first /Tremulous is the folder it's in). Save the file and close it. Now MacRadiant15 should open just fine (with X11 started up already, and X11 can be found in the /Applications/Utilities folder), and Tremulous should be one of your game options. It takes a second to start up, but it'll show up soon enough. If you go to tremmapping.pbwiki.com/GtkRadiantt1_5-Win32 (yes, I know it's for Windows 32, but it works), they'll supply you with all of the necessary files (like the trem.game file and folder), and also a pack of common files which should be put in the /Tremulous/base folder. Oh, also run the pack installer that is included with MacRadiant (on the download disk image). It seems to be necessary for it to work. Further questions about MAKING maps can be found in other threads on the tremulous.net forums.
HAPPY MAPPING!!!
