Whether more memory speeds up a render depends on the complexity of your scene. If a scene can be processed within the limits of real memory (as opposed to being swapped out to virtual / disk memory) then having more won't speed up that particular scene. 1GB is a good amount to begin with; experiment with it before deciding whether you need more based on the types of scenes you want to make.

Decent-quality animations are certainly possible with the horsepower you've got. You'll soon get a feel for the tradeoffs e.g. if you render with volumetric atmospheres, global radiosity, procedural terrains, models with high poly counts and lots of blurred transparency and reflection effects, then animations are going to take ages on almost any machine short of a supercomputer. You'll probably find you can scale back on the effects and still get good animations. Keep in mind that some Pixar movies were done using scanline rendering and shadow maps -- not even ray tracing.

Regarding Poser and Mimic -- Vue won't import the soundtrack from Poser, just the animated model. You'll have to composite the sound back in using a video editor.