"Well, since I'll be getting the upgrade to Poser 5, and since most upgrades require you to have a previous version installed, I'll be keeping my copy of Poser 4" I don't think you need to have P4 installed to use the upgrade. I believe they just send you the full version at upgrade price. (with a big Upgrade sticker on the box perhaps) That's the way it has always been with other progs I upgraded from like Truespace. And that's the way it was when I upgraded from Poser 1 to poser 4. (duh) :)