Unfortunately, it doesn't exist. (Yet.)
I think I've already mentioned that Apple is in the process of overhauling their laptop line(s) and putting in Intel chips. The MacBook Pro is their latest thing, with Intel Core Duo processors; 15" and 17" models are already out. I've played with them in the Apple store, and they're very nice, but too big for my needs/tastes. But ... the old 15" Powerbook was replaced by the new 15" MacBook Pro; therefore, the only Powerbook left on the Apple site now is the old 12". That suggests to me that there may be - no, that there probably is - a replacement in the works for the 12", too.
Personally, I love the current Powerbook design - the way the keyboard runs right up to the edges, thus making the footprint as small as possible, and the way the speakers are hidden in the hinge. I also love the new innovations that are coming with the MacBook Pros, like the magnetic power adapter (so it won't pull your computer off the table if someone trips over your power cord). But the reason I'm still not so thrilled about the rumors that are flying about the newest, smaller replacement (to arrive within the next month) is that it's probably going to be a 13" widescreen MacBook (not Pro). It's not that I don't like widescreen, but I'm not a fanatic for it the way some people (*cough*Dad*cough*) are, and adding a widescreen would be the end of the tiny footprint and right-up-to-the-edges keyboard I like so much. Not to mention, it will probably add to the weight.
Anyway, reports conflict as to whether or not this model will be replacing the 14" iBook, the 12" Powerbook, or, indeed, both. My one glimmer of hope, however, is coming from the fact that the release of any potential 12" models would probably coincide with the back-to-school window, and since we'll probably be seeing the 13" widescreen model in May, I suppose Apple has all the time in the world to figure out a smaller version before September.
Bottom line? Personally, I want a tiny 12" aluminum (not plastic) Apple laptop which weighs 4 pounds and has Intel Core Duo. Apple can stick whichever name they like on it - the iBook, Powerbook, MacBook, WhateverBook - but my wants and needs are really that simple.
Some people are going to wonder why I changed my mind about Apple versus PC. I don't really have an answer for you. Several things sort of coincided and snowballed. I was never completely closed to the idea of a Mac in the first place, because (like the rest of the world) I have an iPod and love it... but then there was the fact that I couldn't find any current PC laptops that I liked enough to buy. And then there were all the cool little features I read about on the Apple website, like the magnetic power adapter and built-in camera and remote control, that I thought were so smart. And the e-mails and opinions I got from various people, telling me how much more stable the Mac OS was. And the fact that the Intel-chip-equipped laptops will be able to run Windows, should I decide I want to. Then, the fact that my sister and I went into the Apple store here in Jacksonville, and I (a) fell in love with and (b) physically picked up the 12" Powerbook display model, and discovered that 4.6 pounds really isn't as heavy as I was imagining it to be. And then, of course, we played with every computer in the store... and what can I say? They're gorgeous. And everything is laid out in a practical, user-friendly way. I had no trouble figuring out any of the applications or settings, even though I've never used a Mac in my life. (Well, okay, yes I have, but the last one I'd used was from the mid-90s and hardly even qualified as a functioning computer anymore.)
...Anyway, I liked them. And now I want one. But it seems I'll have to sit and twiddle my thumbs for a few months while the Apple gurus (hopefully) work their magic on a 12" MacBook.
(Oh, and fijne Koninginnedag to all the Dutch readers... ;))