I think the new 17" Powerbook will work very well with Photoshop, Maya, and Shake. However, XSI will not run on it, because there is no OSX version of it. As far as performance between the G4 and Pentium 4 goes, you're going to find different reports and opinions as to which one is faster. IMHO, if what you're looking for is pure speed and power, then go with a Windows-based notebook. In general, 3D applications run faster on Windows, and you have more options. However, if you want a pleasant user experience (both in terms of the OS and the hardware), go with the Powerbook. OSX is a joy to use and makes XP look dumb and convoluted (IMO), and the physical design of the Powerbook is all about elegance and usability. And, yes, you can use any 3-button USB mouse with a Powerbook (I've used a variety of Logitech mice)
Realistically, it boils down to personal preference and what kind of applications you need to run. If you have to run XSI, then your only choice is a PC notebook. Otherwise, the options are about the same on both systems.
FYI, I currently use an 800 MHz Powerbook G4 (15.2" screen) for all of my 3D and video work, and it has been a wonderful experiece. I still keep a PC around for anything Windows-specific, but I use my Powerbook about 99% of the time.
I have a Powerbook G4 800 (with the 15" screen) and it's quite usable for Maya. However, because I started on the book before Maya for OS X was really ready to go, I have an Athlon 1.4 that I use for Maya when I can.
The Athlon is DEFINITELY faster. However, Maya on the Mac works pretty well, so you might just go with what you like.
One thing to note: using Maya on the Mac without buying a three-button mouse is virtually impossible. I have an external three-button mouse that I have carried around when I have been planning to do Maya stuff, although right now I do not use Maya on my Mac.
As far as a general purpose computer, though, the Powerbook is fantastic. I use mine all the time for just about everything except Maya. When I'm at my desk (like right now) I have the thing plugged into an external 18" LCD monitor, an external keyboard and mouse, and the power supply, and I can completely forget I'm on a laptop at all. Unplug a few connections and go to Starbucks and I'm surfing the web wirelessly. It's tremendously convenient. Sure you can do all of that with a PC laptop but the size and shape just aren't as nice, and I like the Mac OS.
"54Mbps AirPort Extreme — up to 5 times faster
The new 17-inch PowerBook G4 features the hot new 802.11g AirPort Extreme technology — at 54Mbps, the fastest wireless connection available on a Mac. The 17-inch PowerBook G4 comes with AirPort Extreme installed. And since AirPort Extreme is backward-compatible with 802.11b networks — and with thousands of wireless “hot spots” in hotels, airport lounges, coffee shops and bookstores around the world — you’ll be able to use your PowerBook G4 to get online from practically anywhere."
Wireless options are similar between Mac and PC. Both support 802.11b and 802.11g, which are fast (10 to 50 Mbps) and require that you be in the immediate vicinity of a base station. Alternatively, you can get wireless modems for either system that will let you dial up over a digital cellular network at a much slower rate, currently about 50-75 kbps. These can be used over a much wider area as they're based on digital cellular telephone networks rather than specialized 802.11 base stations.
In answer to the original question - I'd go with whichever platform they use at the university (which is most likely to be PC).
If your wanting to take work home you've been doing in the uni labs and vice versa its a good idea to have the same platform. Whislt maya files in themselves will work on either, there are a lot of plugins (not sure about scripts) for maya and shake that arent available on OSX, and whilst its a very nice operating system, unfortunatly its still yet to be widely accepted as a serious 3D production platform.
I'm guessing this will change over time, but thats how it is right now.
Well, if you're writing or using lots of plug-ins, that is a point.
However, if you're not, you should pick the laptop you like best and forget about platform.
Moving Maya files between platforms (including MEL scripts) works fine, except for plug-ins. When I was working on the book project, I'd do some work on the PC and then load it all up on the Mac and go for a coffee... finish the work there, then move it back to the PC again. At the time the only weird thing about this was that the Mac was at version 3.5 and the PC was at 4, but now even that issue's gone.
BTW, most universities have plenty of support for Mac users, at least here in the U.S.
The uni i was at (in the UK) did have Macs in the labs too, but they were more for video editing - the actual 3d lab was PC based (with a few old O2's aswell ).
Since my post has stirred up an :argue: icon from you let me elaborate a little-
The reason i bought it up was from (indirect) experience - there were a few mac guys on our course and they had no end of trouble getting work transferred across when they got back to halls in the evenings as we were doing some work in Live (which as I'm sure you know isnt available (yet) on OSX). This caused a whole lot of hassle for both them and the staff..
Aanyway - it'll be worthwhile checking before hand if the course consists of any Maya Unlimited specific work just to be safe.