I have the video (DVD) playing on monitor A, but when I go to fullscreen, the video pops over to monitor B. I've seen other threads with tips on where to set the video device, but those menu options don't exist for me! I'm running "VLC media player 0.8.6 (wxWidgets interface)" on Ubuntu Edgy. Oh, another thing that is probably relevant: my window manager is Beryl (the OpenGL 3D manager).
In fact, I just did a test. I switched back to Metacity window manager and the fullscreen goes to monitor A. Even if I had the video playing in a window on monitor B.