Try not to get imported meshes into heavy ecosystems. Eran Dinur's eco didn't have imported objects, and most of them were trees (it was Cerdo Verde, right?) that V5I heavily optimizes, so that isn't taking much RAM.
Animation, as I can tell, isn't really different than stills. You just have to be smarter and get everything static done in the first place and animate in box mode. (That's for me, working on a Athlon XP 2500+ and 768MB of RAM)

In This Twilight- My FIRST public poser work in 2 years!
Also the reason why I endorse postwork (:D)