Get a Mac. Write it off.
Seriously - Macs are junk for gaming, but made for this sort of thing because they just don't crash or require heroics to keep running. My parents have one and they ask me for computer "help" maybe every 3-4 months as opposed to every other week with the old PC. Guaranteed, you'll spend half the time dealing with maintainence issues, and if the PC is acting up, you're not running your business.
I've used Macs for photo editing for well over a decade and 10 years ago, I would have agreed with you. These days, I can't. I have a fairly old P4 running XP that has proven to be a very solid digital imaging box. I've used it for portrait, landscape and scientific photography and it has performed extremely well. It has also functioned as the family office PC, the kids have gamed on it and we have all surfed extensively on it. I'm typing on it now in-between projects and I've got 8 windows open, including Photoshop that has a big pile of 60MB images open. This box runs great and is not a maintenance hog.
I also have a 4400+ based rig set up for photo and video editing. It is much faster than the P4 and has a better setup WRT storage. I still work on my own and customer Macs including big expensive Macs enough to know that they no longer offer me any real advantages - and they are super expensive.
Bit of trivia: Adobe first made its software for Macintosh. Their Windows versions are always a bit hand-me-down as a result. I've used Photoshop on both systems and the Mac version is a good 20% faster and easier to use, mostly because of the lack of Windows background processes and bloat-ware.
I took my third Photoshop class recently and talked to the Adobe instructor about this very topic. He claims that your story line used to be true but has since evaporated into myth. He told the class that by the time of Photoshop 6.0, the Windows version had been made fully native PC code.
With the advent of the newer OSes, Macs also crash a lot less often and actually recover from them far better. "Let me reboot the machine"(Windows) versus "Let me run that again and try a different setting".(Mac)
The 4400+ machine I mentioned above has had to be restarted a total of one time since I assembled it over 7 months ago. This bit of Mac hype is meaningless. Sure, it makes for great TV adds, but if you know how to set up XP properly, it is a very stable OS.
Look, I fought for and won approval to set up a Mac network across a large global imaging group in the early '90's, then got the support to upgrade it in the late 90's. I love Macs, but the truth is that they have lost the advantages they once had. I still sense a slight edge in high res video editing with a G5, but that's just not enough to keep me spending so much extra on them. Now that Conroe is coming right around the corner, it's game over in my opinion.
I've done both and wouldn't run a business on PCs unless I had no other choice(SQL or simmilar being required).
Likewise, and I come to the opposite conclusion. Your comment about PCs crashing makes me suspect your ability to set one up to run XP. That's not a flame, but XP is a stable OS and if you know how to customize the setup (hint: don't buy a Dell network of workstations) then PCs can and do run efficiently.