Well... just so you know, btdownloadgui IS the GUI version, sure you have to launch it in the commandline but it will open up a GUI for ya. Anyways if you want command line, you're looking for btdownloadcurses.py. Also are you sure you are putting the full path for the file? For example if you are in the BT directory you should type:
$ btdownloadcurses.py ~/path/to/torrents/battlefield1942.torrent
My guess is, you aren't providing the full path so there isn't that file in the current directory. You could always just have your browser launch btdownloadgui when it downloads a .torrent file.