Usually the term “compositing” is used for the variety of tasks that are done to get image sequences layered together into a “composition,” not to be confused with “compose” for music, and “compost” for gardening. ;>) The “higher end” VFX houses use Nuke, Shake, Fusion, etc. for this aspect of the pipeline, but Blender has an excellent set of tools built right in to the program, and the newer development for 2.5 will be adding polish and more node control to this aspect. It can be very useful to bring in a variety of render passes, generated out of Blender also, and to be able to control the contribution of each pass to the complete composition. Blender also has a Non-Linear Video Editing capacity, but it is not as robust as the Compositing aspect and provides different functions. There are tutorials over on Blender.org, and you can always search around on BlenderArtists.org for related topic threads that will generate leads to tutorials also.
For those who don’t know about it, there is a fine development of an Open Source Compositor, currently Linux only, called Ramen, over at http://ramenhdr.sourceforge.net/. I am trying to get the compile worked out for Win32 also, but it is being developed by an individual with a good background in VFX Compositing, so take a look, download and try it out.
Paul