Why does the game run so sloooooow?
Will it run on my P166 with a S3 4Mb gfx card? No, you need a fast cpu and prefferable a 3D card. If you want you can try the software-rendering version which uses the Allegro library.
Is there a level editor?
Why doesn't the rpms work on Mandrake?
Why are the sounds delayed with 0.5 seconds?
You're either using arts, esd or have buggy audio drivers. Stop arts and esd, if that does not help install alsa drivers.
Why can't I hear any music even if I hear the sounds?
The game uses the default midi player of SDL_mixer, 'timidity', which is compiled into SDL_mixer. You can compile SDL_mixer yourself and tell it to use native midi or something. First check that your system is able to play midi files, use 'kmidi', 'timidity' or something. Then you have check that SDL_mixer can play midi files, the name of the program is 'playmus'.
Things that might fix your problems are: fiddle with the /etc/timidity.cfg file, use latest version of SDL_mixer, compile SDL_mixer yourself, use alsa drivers (I always recommend alsa drivers). I'll give more answers when I know more about what causes these troubles.
Compiling the editor complaines about moc_* files?
Your version of QT is different than in the package. Simply delete all moc_* files, they will be regenerated.