If I'm not mistaken... PS8 is CS. CS just stands for Creative Suite I think.
According to the Adobe Website, Creative Suite II contains Photoshop-CS2 PLUS other programs (this quote is from the Adobe website):
"Adobe® Creative Suite 2 Premium software is a unified design environment that combines full new versions of Adobe Photoshop® CS2, Illustrator® CS2, InDesign® CS2, GoLive® CS2, and Acrobat® 7.0 Professional software with new Version Cue® CS2, Adobe Bridge, and Adobe Stock Photos. Delivering the next level of integration in creative software, Adobe Creative Suite 2 enables you to realize your ideas anywhere — in print, on the Web, or on mobile devices."
if you bought is AFTER they announced CS2, then you'll get it for free.
Or if you bought it JUST before.
I got mine end March and, on speaking to Adobe Customer Service on the phone, was sent a free copy of CS2. I also mentioned that I was disappointed that already the latest versions of the Camera Raw plugin were not compatible with CS, only with CS2.
At this point, I can say that the most important differences between 8 and 9 IMO is the treatment of Raw files...PS9 is a major step in that direction.