QuickTime Pro ($30, from Apple) lets you do that and lots of other do-it-yourself assignments. There is no "Brady Bunch" command, of course, but QT Pro, which enables the movie-editing features of QuickTime Player, lets you easily build a "sandwich", containing whatever layers of video and images you want, each playing any size you want, playing simultaneously or in turn.
Just two days ago, in fact, I built a Brady Bunch grid containing twelve -- count 'em, twelve -- H.264-encoded movies. (I wanted to test how well a bunch of H.264 movies would play on a Dual 1GHz G4.) Smooth as silk, without a hitch.
After building the movie grid in QT, you simply export it to a DV Stream movie that you import to iMovie. Essentially, that "flattens" the image so it's back to one movie track, which plays like any other movie.
Remember, any clip (or combination of clips) you build in iMovie can be added as a layer to your grid/sandwich. So if you want a layer that contains clips that fade in and out, build the clips in iMovie, export them from iMovie to a DV Stream, open that in QT Pro, Copy it and Paste it in as a new layer of your sandwich, or a new element for your grid.
Lots of possibilities.
Karl
