zescanner:
*I am interested in a laptop primarily for the benefit of being able to take it with me a do my 3D imaging wherever I happen to be, rather than being tied to only doing it when I am at home (which explains why my gallery here is so small).

If laptops are really at a noticably lower performance than a desktop then I will not go that route.*

These are contradictory considerations, but perhaps point to the essential decision you must make.

If the real limiting factor to your creative output is being away from your computer for extended periods, then I would suggest it doesnt matter if a portable computer is slower than a desktop computer. Youll create more with a computer that is half as fast as another which you can access only one tenth as often. Theres no sense in having a super-fast desktop PC if you cant be on it most of the time.

Assuming that computer access time really is the deciding factor, then a desktop is out of the equation and your real choice is between types of portable computer. Fortunately, the latest technology laptops / notebooks are not too far behind an average desktop PC in performance terms.

With that in mind, my advice is to go for the fastest and best Intel Core Duo laptop you can afford even if that means buying an Apple Mac. While a Core Duo might not be as fast as the fastest desktop replacement laptop in terms of pure Bryce render speed, the fact that you can do other activities (3D modelling, Photoshop, surfing Renderosity) on one processor while Bryce is rendering on the other makes the parallel processor much more useful.

The most important aspect of your 3D imaging is you. If youre not there, the fastest computer in the world might as well be the slowest.