Poser5 has a whole selection of Poser4 models and props, but I would say yes that it will read the older runtime folder items with no problem. The improvements and additions to Poser5 are HUGE! It is a completely different beast, the texture generating application built into Poser5 is the same that Mac users have enjoyed with, Pixels 3D which is also where the Firefly render engine came from as well, that alone aside from all the dynamics are enough to upgrade. Super stuff! However there are a lot of the plugin things (if you have invested heavilly) that may need updating... ie., special clothing and hair and morphs and stuff like that. The other major thing to consider is that it takes a considrable amount more CPU power so you may after getting it be forced to upgrade your box... I don't know what you have. Otherwise I'd say "Go for it!". You'll be glad that you did.