I agree with ynsaen poser 4 and poser 5 should be installed seperately as two seperate programs, you can still use the poser 4 stuff in poser 5 if you add the runtime to poser 5. You could use the poser 4 renderer in poser 5 if you don`t need the firefly renderer things. With poser 5 you can make the water have real reflections and with service release 3, the atmosphere tool is good for volumetric lights (the type where you see the beam).