Let's ignore XMBC, as we can't control exactly what it is doing.
Once you get things working correctly via cmd.exe, then you can take those commands and see about getting them to work when launched via XMBC. In other words, remove the extra source of problems, and get to the core of how the command line commands work. Once you have these figured out, and are confident you can get the movie playing, then you can try using other launchers.
It seems like we're chasing two problems here: 1) the movie does *not* play. 2) the movie plays in display mode, but display mode is not fullscreen.
Display mode can be full screen (maximized), or windowed. Is it that you're seeing a windowed Display mode, and not a maximized Display mode?
Perhaps you can share exactly what commands via cmd.exe you execute and explain the results. As mentioned, the commands given in the first response *do* work. If they are not working for you, we need to see exactly what might be going wrong. Unfortunately, "the movie doesn't play" does not get us any closer.