add the following line to the state=0-lines of your loadgame.ini/fpi for the specific level.
:state=0:playfullvideo=files/.../...
look into the script syntax list by ched80 in the sticky on top of this subforum for more commands.
please say that you know where loadgame.fpi is located.^^
(languagebank/english/gamebank/mygame/.../ is standard)
you have to test the codecs of the video you want to load (no xvid, it uses an external decoder that crashes fpsc). i dont think anyone has found the best solution for compatibility and playability yet.