gchuck,
I ran P5 and P6 for a few years on a 2Ghz P4M, with a 32mb GeForceGo 460. Initially it had 512mb RAM, but I had to be pretty conservative about what I put in the scene. After I upgraded to 1Gb RAM, things ran much better! I'd recommend upgrading your RAM, but you'll be able to use it as is, it just might be a little sluggish.

drifterlee,
Go for it!  The use of system RAM will slow things down a bit, but with your system specs, Poser should run very well. With P7, rendering performance with your dual core processor will be very fast. You will get a little better performance if you can optimize XP, the rich media edition consumes quite a bit of RAM. I recently got a HP laptop with rich media edition (and a lot of other junk HP installs on the system) and straight out of the box it was taking over 450mb of RAM.  I shut a few un-needed processes down, and uninstalled Norton Secutity Center/AV, replaced it with AVG, and got back over 150 mb (norton was using over 100mb).

__________________________________________________________

My Rendo Gallery ........ My DAZ3D Gallery ........... My DA Gallery ......