3DVIA Composer has a "Video" button that will save your animation sequence to an AVI file. This method is very easy to use, and is the place most people go when they want to save their animation to a standard movie file. This method, however, is meant to be for quick video creation and doesn't provide the highest-quality results. Dumping an AVI directly out of 3DVIA Composer also makes for an inflexible, single file that doesn't allow for easy post-processing, such as overlaying on a custom background.
When using professional 3D animation software, there is another method for output that is much more common: individual frame output. This makes a series of individually-rendered image files that can then be brought together in a video compositing application, such as iMovie or Windows Live Movie Maker. We can get invididual frame output from 3DVIA Composer, which offers a few key benefits: you can use all the output options available in single-frame high-resolution rendering (which is why you get higher-quality imagery) and you can save an alpha channel in the frames, which allows for a transparent background.
Consider also that professional videos typically have a soundtrack, custom backgrounds, titles, and multiple video sequences with transitions. This is the realm of video compositing and editing software, not 3D animation software. Windows Movie Maker can do some basic effects and titling, as well as save videos in a number of Windows and web-compatible formats. So even if you are just getting started and have zero budget for new software, you can really polish your output.
The basic technique is to use the Multiple tab in the 3DVIA Composer High Resolution Image Workshop to make a series of images out of your animation. I like to use 24 images per second:
The result will be a bunch of image files, numbered in sequence 0 through whatever number of frames are required to capture your animation. Then, you make a new movie in your software (I'm using the free Windows Movie Maker in my example here) and add all of the image files into the empty movie timeline (in order, which is easy to do in most software).
Once you bring the images in, select them all and change their display duration from whatever the default time is (in WMM it's 7 seconds) to be the fraction of a second each frame needs to be in order to playback in real-time (1/24 in this case, or .041 seconds). Then, when you play your movie timeline, it'll be the right length instead of slow motion.
Windows Movie Maker allows you to add titles, other clips or still pictures with transitions, and an audio soundtrack. It also has some basic post-processing effects that allow you to manipulate color over a range of the movie (or the whole thing) very easily:
If you want to have custom backgrounds or "picture in picture" -type effects, you'll need an inexpensive but more capable video editing tool such as Sony Vegas Video Pro ($99). Once you learn the basics of inexpensive video editing software, you'll never settle for static unfinished movies again!