Frankly, Ive never liked the idea of rendering a MOV straight out of Poser, just because of the way Poser does it in one big shot. The machine becomes useless until the render is done, and I just can't afford to lose that kind of time on anything. So I render as a stack of pict files and then put in something like Moover to create the movie file. That way, I can stop the render any time I like without losing any of the work to that point, and if Poser kacks about memory (which I suspect may be your problem), I can reset and continue afresh.