regarding Red Baron's original question: I can think of one problem you might have with both P4 and P5 installed on the same machine. More of a glitch than a problem and I can't speak to MAC as I only use PC. If you want to call a PZ3 file or some other file unique to Poser that P4 and P5 share, the default in the registry may not point to the path of P4 but rather to P5. This glitch may be ok as long as you are aware of it. - TJ