When I try to render to .avi in Poser 5-SR3, my PC STILL crashes and does a memory dump. Has anyone figured out a way to avoid this?

I render to image sequences, myself. If it crashes, I can restart Poser and pick up where it left off. When it's finished, I compile the images into a video. Probably not the answer you wanted, but Curious Labs is allegedly working on another service release, and DAZ Studio is due in a few weeks.

P5 has a lots of memory leaks. One bad one in particular concerns all textures loaded. Even if you're not using a texture in your scene it stays laying around. P5 can't handle lots of MTs either. I have MT reduced figures that I use. That may help you. For example, doing a movie with full V2 loaded with MTs will probably cause you to belly up pretty quickly. I have created a stock V2 with a single Body MT for her shape so the only MTs she has is that Body Morph, the facial expressions and the stretch legs. I can go a lot farther between shot down and restart before I crash than with a fully loaded figure.

If you watch how the pros do it, most camera "scenes" are short, usually 10 seconds or less. The way L.D. says to do it and bearing in mind what Mason said will help, but also keeping you camera scenes as short as you can and compositing later on in another program may help too.