Pheewww!!!
PhysX add-ons just got announced, and it was a close call. Oldest compatible model seems to be 9600 GT.
So I was close to purchase only non compatible cards. At least I will have one to play with the PhysX toy.
PhysX is refering to coprocessor(s) dedicated to objects motion calculation (according to the laws of physics).
Removes a lots of work from main CPU's/GPU's when it comes to render a collapsing wall or floating cloth.
EDIT:
I probably misread the article. I doubt low price cards will be compatible with it. No PhysX fun for me! (oldest compatible model seems to be 9800, but specs are still a bit vague)