The AppleCare for MacBook Pros is also good for PowerBook G4s. At least, that's what I understand from the website.
You could ask at an Apple Store and see what they say, or call AppleCare. You might still even be able to activate it, but it will take effect from the day you purchased it. (What it says on your receipt).
Also, if you bought the AppleCare when you bought your PowerBook, it should have been automatically registered and activated (if you bought it at the Apple Store).
See this link and you'll see what I mean about AppleCare being the "same" for MacBook Pros and PowerBooks:
http://store.apple.com/1-800-MY-APPLE/WebObjects/AppleStore?spart=MA515LL%2FA
Message was edited by: Pismo 900
I highly doubt you could get a refund at this point, since the latest you could have bought a PowerBook brand new was in 2006 (unless you got it in 2007 and the PowerBook you bought was brand new in box and never ever registered) and a year has passed already. Usually refunds are 30 days. Apple has a 14-day return policy. I think your best bet is to save it and see if you can transfer it for use on a new Mac portable (if you choose that route), or, see if you can activate it on the original Mac you purchased it for.