In season one, she used the original Powerbook G3, if I'm not mistaken (it was either Kanga or the 3400c), but she moved up to a WallStreet and then a Pismo until the series concluded its run.
The official website for the movie has added a new feature, "Carrie Bradshaw's MacBook Pro" that allows fans to "explore" the virtual desktop of our favorite fashionista, answer trivia questions in "chat" windows with other SATC characters, based on clues found on the desktop, to unlock bonus content/videos and for a chance to win a Sex and the City movie poster.
I'll admit, the whole thing is a total novelty, but it's still kind of cool. I especially like that the default browser on the "desktop" is Camino. It's always fun to see Apple products integrated into other promotional campaigns.
(New Line Cinema, like TUAW, is ultimately part of the same media conglomerate, Time Warner).