Hi Trisha -
I was wondering if you could clarify the nature of your concern a little bit. Is he looking for something that he can edit with, both at school and at home? If so, schools across the country use a mixture of Apple editing suites (Final Cut Pro) and Windows editing suites (Avid.) Almost every school I've looked at has both. Either way, your nephew can run both mac and windows editing solutions on a Macbook Pro, as one can run both OS X and XP/Vista, if so desired. Though it comes down to personal taste, he'll probably find that Final Cut Pro to be both extremely powerful and it comes with a more user friendly interface. Final Cut Pro is rapidly becoming a professional standard in the "industry"; note Little Miss Sunshine and No Country for Old Men both are two recent examples of films edited with FCP.
However, when you talk about people like Spielberg or Cameron, you're talking about people who have the best of the best equipment, with access to software and hardware that many schools don't even have (excluding the major USC, UCLA, NYU etc., who seem to be very well endowed...)
On the other hand, if your talking about the kind of computer these people are liable to use, say to communicate electronically with their cast and crew, you're likely to find a more window's centric environment. Again, no problem here with the MBP, just load XP or Vista on its own partition and boot into it whenever windows environment is absolutely needed. You'll find that most software these days (at least for e-communication) are becoming cross platform compatible.
I'm a struggling film maker/photographer my self. I edit fine on my MBP using the Final Cut Pro studio. For motion graphics, I've never found myself limited by Adobe After Effects. In fact, both Adobe After Effects and Photoshop will be extremely useful tools in the editing process as well. In the end it just comes down to how much money you want to spend, and whether you have a preference to be on one platform or the other (or both if you want on the MBP.) You won't be disappointed doing graphic work on the MBP, personally or professionally, in my opinion.
Hope that helps,
Jared
