Poser 5 is a great program but if you are doing proffessional animations then you will find the firefly render engine much slower than P4. However the improved end results are worth the wait particularly when using procedural shaders. Have you looked at the possibility of exporting BVH files from Poser into another program. I assume you could bone and joint Poser figures in other high end software and end up with faster rendered animations and higher quality too. I've never managed to get P4 and P5 running at the same time and I can't really see any reason for doing so.