There's another advantage of P4 over P5....you can import Pz3's from P4 to Vue....you can't in P5 (at least not yet). If you don't have Vue and don't intend to get it and have a high end computer (ooops....just saw your specs), P5 is probably the most cost effective way to go. Having now seen your specs, you may be better off with P4 or Pro-Pack or doing what Judith suggests. Since I'm not a fan of upgrading Operating systems on machines that may not be designed to handle them properly, I would recommend XP Pro on a new machine if you can swing it. Poser 5 seems to have the best results on the XP machines (probably on any NT based machine). Definitely don't miss those blue screens judith! :) I have P5 (never had P4) on a P-IV, 1.7 ghz processor, 512 mb ram and XP Pro. Regular renders are fine, but when you start adding a lot of characters and textures, you push the memory limit to the max because of how P5 handles memory. Fortunately, XP Pro is pretty smart and "reallocates" enough memory for you to get the job done. I don't even try to mess with the hair room.....way too slow on my machine. I've also learned to find work arounds for the few annoyances that remain in P5 (after upgrading to SR1). I like the material room frankly and the ability to nest directories and have multiple Poser runtimes. The later seems to help improve the speed of the program.