15" Powerbook?
One option would be iBook and iMac. The iBook is rugged, has great battery life, and will handle mostly anything you put it through. And you would have an iMac G5, which will handle any audio/photo/video editing you through at it.
Another consideration, the one I'd choose, would be a 12" or 15" powerbook and an external display. One big reason is because you always have your files and applications in one place. For example, if you wanted to get microsoft office for both iBook and iMac, you would have to either have to buy two version of the standard edition or buy student and teacher edition, which can't be upgraded. It tends to be easier not to have to sync comps all the time.
Definately stay away from the 17" powerbook. Don't get me wrong, it's is a beatiful laptop, and definately apples strongest leg up from the PC world (17" PC laptops tend to weight between 8 and 10 pounds, and be 1.4 and 2 inches thick; 17" powerbook weighs less then 7 pound and is 1" thick). It's just too bulky to travel around with regularly. If you want considerable power in a VERY portable package, the 12" is slightly better suited, but in my opinion, the 15" is perfect. Almost as much power as the 17" in a smaller frame (vs. 12" which lacks a lot of what the 15" does), and still a lot of screen real estate for your apps.
One last thought to point out. I don't think it's worth it, but if you choose the 12" powerbook, you will have enough for a 20" apple cinema display, and you might think it worth it.
Good luck with what ever you get.
The best,
Switchr