Your talking about Photoshop 8.0 CS aren't you?
Christ I've had serious problems with that version, the problem is Adobe tried to instil a version of the software that only accepted certain keys. A little hindsight could've been needed to the fact that they released it late in the year, and the authentication is based on the year you do it.
Now you can just clock back your date to 2003 and install it with the code. It will install and run fine, problem is when you boot it up once turing the date back to 2004 it'll once again complain.
You have to get the Authentication Patch from the Adobe site, (you'll need to log-in using your premium account) and install that while you've turned your clock back to authenticate it in the right year.
After that things should be fine.
I hope they sort a better system out for 9