That's pretty odd, I remember reading several stories on this very forum about people who called about 2 weeks later and they were able to exchange theirs for the newer product. Maybe you should try going in and talking to someone (in my experience, younger guys are the most sympathetic to other younger guys...assuming you're a guy, Prissie...if not, then a younger girl) in person. Maybe even a manager, and bring your mom too, they might feel more sympathetic. Like Padawan said, it's not good business for them to "cheat" you like that, so perhaps they'd make an exception, or maybe the lady you spoke to didn't quite know the rules. If they agree to, make sure you get their name so when you come back to the store with your powerbook and the person isn't there, you can atleast say whoever it was told you so.
BUT...if you're not able to return it, well **** a 1.33Ghz 15" Powerbook is not only a super nice machine, but it was the fastest puppy around until 2 weeks ago, it's still better than 90% of what other mac owners have, and you're still the envy of many, many people. I've played extensively with your exact computer, and I own the 17" 1.5Ghz Powerbook, and lemme tell you honestly? There isn't THAT much difference. Sure, maybe a few more frame rates in games or a couple hairs of a second less in photoshop rendering, but in all seriousness, that's NOTHING. You're PB is the same as mine, dude. Or dudett.