Compressor is the best solution for this problem, however it can be a bit complex at times, especially switching from 16×9 to 4×3. There is a droplet that would work for you but I’m on my iPad right now and can’t check it out. If you just want the quick and dirty solution then try this
-In FCP switch your Easy Setup to NTSC DV or whichever SD codec you want.
-Create a new sequence
-Put your footage onto that timeline
-Say no when it wants to adjust your timeline to match the footage
-Adjust the distort and size parameters to what you want (double click the clip, third tab in the viewer)
-File->Export->Quicktime Movie
-Make sure that “Self Contained Movie” is selected
This is the quickest and dirtiest solution.
Shoot sh*t, Edit sh*t