A Mac Pro is a great machine to build on. You start with quad processors (2 dual cores), with space for 4 SATA hard drives, 2 optical drives and 16GB of RAM.
The reason you don't want a Mac Mini or Mac Book for editing and high end graphics apps is because they don't have a dedicated video card.
The problems with Adobe Photoshop on Mac Intel is that it has to run under emulation. I would expect a Universal Binary of Adobe Photoshop soon. However, you might consider one of the bundles offered by some of the Mac vendors where you can get the Mac with Parallels and Windows XP installed, or Windows XP setup for dual boot. As long as you stay off-line on the Windows side, I wouldn't think you'd ever have a problem with it. If you use Parallels Desktop, you can run Windows in a virtual machine, while running other Mac software. The best part is that the entire Windows system exists as a file on the Mac that can be backed up and restored with a simple drag-and-drop, so keeping Windows running becomes very easy.
Essentially, when purchasing the new Intel based Mac, you need to see if your favorite apps have Universal binaries, or consider running them in a Windows virtual machine.
You can't go wrong buying the Mac Pro. Even if you use it to run Windows (???), it is an excellent piece of hardware. Extremely powerful, expandable, and capable of running anything out there.
BTW: I have a dual processor G5 and two Intel Macs. I've had no problems with the Intels, yet, but Photoshop runs like a sick cow on the Intels.