If you are on linux open up a terminal and type "which tremulous" which will then tell you what is running when you try to start trem. Open that with a text editor. If all you see in the text editor is several hundred lines of garbage, its probably you're tremulous executable. In that case you'll have to rename the executable and make a shell script in its place.
If you're on windows, dave's tee statment won't help you. If it exists you might try setting the cvar cl_autorecorddemo which will provide you with a demo, which you should be able to convert to a condump in-game.