For what it's worth, I use a dual G5 Mac with a couple of gig of RAM. My monitor is a 19" NEC CRT that I run at 1600x1200. I still prefer CRTs for images because of their high contrast, but LCDs are getting better all the time. Maybe by the time this monitor croaks I'll have a nice LCD. I think the advantage to the Mac is that color calibration is an essential part of the system, so once you've calibrated the monitor your colors stay true (at least as far as the gamuts overlap) all the way through printing. I didn't mention printing. If you actually want to print your images, you'll want to take care of that part of it. Most reasonable quality inkjets will do a pretty good job as long as you use high quality glossy paper. The problem is that dye based inks (such as my older Epson model) will fade after a year or so. My wife has an Epson pigment-based printer that gives nicely saturated images with much more stable color. Of course as anyone with an inkjet knows, filling the blasted thing up with ink costs nearly as much as the printer did in the first place. Still a lot cheaper than keeping a sports car on the road.
You are right, the image processing software is the 'other half' of the camera and a good fast computer w/ ample memory really does help. As for image purity, I've seen that the Macs are much better for color and detail. I use an iMac 20" model w/ 2 GB of ram, it helps and of course Photoshop CS2 (CS3 is in public beta testing) for for most of my commercial work and getting to the point of being able to use it all to produce a good astro image takes some time too. But it's a great way to enjoy life and see the roses.