What version of photoshop and operating system are you using?
C3 windows 7
Sent from my iPad
I don't believe the Registration from inside photoshop cs3 works any longer.
Turn off your internet connection and just click on the Never Register button.
If you already registered cs3 before using your other computer, there is no need to do it again.
(if not, you can log into your account and do it there)