Mac or PC for photography
Notice that I said mac OR pc. Not versus. The Mac OS is a highly stable system, however, it will crash (kernel panic) when hardware is bad, particularly bad RAM. Get good RAM and lots of it, especially for Photoshop. Also know that Photoshop is for image editting and manipulation and is considered the best at what it does. However, as a photographer you will probably want to evaluate (then purchase) Aperture, made by Apple for the professional photographer. The second iteration of this software is absolutely awesome! iPhoto (part of the iLife suite) is alright for amateurs, but Aperture is what you want.
As for running Windows on Mac, do it! however, not only can you use Boot Camp to create a dual-boot, Mac-Windows machine, you might want to consider using Parallels Desktop, VMware Fusion or CrossOver, instead to run Mac and Win at the same time. (I prefer Parallels Desktip.) This way you can run the great Macintosh apps, then fire up Windows XP or Vista or 2000Pro (and more) when you want to use those few Windows specific applications that you might need. By the way, just because Windows has thousands more applications, most of those are on the low end and on the gaming side or are very specific to a particular niche - 95% of which you'll never use. Most businesses use no more than 20 applications on a single machine, and most businesses don't use half the power of MS Office. Save yourself money, don't buy MS Office. Get one of the inexpensive Office clones from Open Office Org (such as Neo Office) or something similar. As a photographer, you might prefer Pages (part of the iWork suite) for professional looking page layout without the huge expense - AND it can export as PDF, Word, HTML and other formats. Use that monetary savings to pump up the RAM in your machine.
The iMac 24" is considered an entry level 'Photoshop' machine. The Mac Pro is considered the machine for the professional; however, it isn't cheap and you have to add a monitor. Don't get a cheap PC monitor that can't be color adjusted! If you want professional results, get a professional display (which doesn't necessarily mean expensive -- check out the CNET reviews.)
'Nuff said. If you want more advice from a professional consultant in your area, check out http://consultants.apple.com