Poser Pro is a more professional version of Poser 7. It has some features like gamma that showed up in Poser 8, but it mainly adds:

o a 64 bit render engine which rarely runs out of memory if you have a 64 bit OS and tons of memory. (I have XP Pro 64 bit and 8GB.) If you don't it's useless.

o background rendering. Start a render and then work on something else. Good for the final render, but for the test renders I just want to see results without losing my focus.

o network rendering. If you have more than one computer, you can let them all help!

Bottom line: if you have a bunch of computers or one with a 64 bit OS and more than 3GB memory then I suggest Poser Pro. If not then Poser 8.

(Apparently if you have Poser Pro then you can upgrade to Poser 8 and the cost will be deducted from the Poser Pro 2010 upgrade price, so if you want to get Poser Pro and upgrade to Poser Pro 2010 then Poser 8 is free. This was the deal for former Poser Pro owners, I don't know if it applies to new ones.)