Your warranty is with Apple, not with the dealer.
When you buy it, if it is new and sealed in the box, you get the warranty. Period.
You then register it with apple (I'm sure they ask where you bought it, for marketing purposes) and your warranty clock starts ticking. But if it's new in the box, authorization doesn't matter. The warranty is by apple, you can't read the terms and conditions if it's sealed in the box, so how would YOU know that Apple won't stand behind its products? That's not YOUR burden, is it.
Check Apple's website for a copy of the warranty that comes with the ibook. If it has a clause about authorized resellers in it, then you have to make the call. If not, then hubba!