As a professional photographer I have much the same opinion as Gunbei. I have a Mac dual processor tower and the new 17" Powerbook. Both are excellent and you have the choice of several operating systems.
I have OS 9.1 on one hard drive in the Mac tower and OS X Panther (plus OS 9) on the other hard drive. The Powerbook is running OS X Jaguar.
For those who are accustomed to Win machines, the software that makes them so valuable in the business world is also written for Mac. I have Microsoft Internet Explorer, Word, Excel, PowerPoint, and Entourage.
As Gunbei pointed out, Photoshop and Illustrator are native to OS X and not only run faster, they never crash. With each Mac, comes photo viewing software called I photo which is the "visual" counterpart to I tunes and the I pod.
If you install the editing software provided by Nikon or Canon, the Mac software recognizes it and allows the user complete control over where to view, edit and change images. The FireWire port on Mac will allow you to plug Nikon directly into the computer and control it from the desktop. Handy for time exposures, delay flash or astral photography or a situation where you wish to be remote (or in the comfort of your car).
As for Cameras, I don't know your budget but the new Nikon D70 is pro quality for reasonable price. I suspect it will sell for about 1K. Here is a link to a new test and review:
http://www.kenrockwell.com/nikon/d70.htmGood luck with your venture whatever way you decide to go.