I don't want to derail this into some Shog-infested Mac vs. PC thread, but I'll make a few notes:
1. "Style over substance" is wrong and ignorant, if anything. Style may play more of a factor, but it's more akin to "Substance with style". What you can do on a PC, you can do on a Mac.
2. The move to Intel chips shouldn't affect anyone's purchasing decision as the transition to most users will be transparent. Applications will still run and still work with no noticeable difference. For 90% of consumers, this isn't news of any significance.
newsguy: My only concerns with regards to an iBook is what kind of video editing and use your girlfriend does. If it's casual use all around, a 12" iBook should be fine, but as you're aware, a real deal video editing laptop is pricey. The advantage to the iBook or an Apple laptop versus a PC one is that you get a bunch of great, preloaded software including iMovie and iDVD which you won't get on a PC, so do take that into consideration. I'd recommend at least going into an Apple store if there's one nearby and getting some hands-on time with the iBook and grab an Apple rep if possible or just go to a retailer that carries Macs and try it. You know your girlfriend better than anyone here, and I think playing with it firsthand should give you a good idea of what to expect.
I think HDD space is somewhat secondary really to the RAM and graphics card for video editing since you can always grab an external HDD. Unless a lot of the video editing is going to be done in places like a coffee shop and other miscellaneous places, an external HDD shouldn't be much of a hassle if most of the editing will be done at home or the university.
That said, you must have a hell of a girlfriend to buy her a laptop. Congrats.