I have recently made the "switch" but my case is a bit different.
I grew up with a lawyer dad (Windoze) and a teacher mom (Mac). I was raised on both, and since i'm a total computer nerd, I geeked out at a young age and learned everything about both systems. When it came time to make an informed decision about which I was going to buy for my own personal use, I chose PC. This was about 10 years ago. at that time, I think mac was on OS 7 or so, and it was TERRIBLE! I always made fun of my mom's Mac's etc.
Fast foreward 10 years, and here I am sitting in bed typing on my MacBook Pro. What happened? Mac OSX simply blows Windows out of the water, HANDS DOWN. There is no messy registry to mess with, the system is not based on and relient on one program (Internet Explorer) and the support and product is just a step above. Mac has always had the upper hand in graphics, and that was one of my influences to switch. I was put on a project where we had to do a LOT of video editing and run a show with a ton of video clips. It was all done on a Powerbook G4. I got my Powerbook shortly after that project. I traded that to my mom for the MBP for my graduation present. Everybody won.
I run a lot of intensive programs on my laptops. CS2, Lightroom, VectorWorks, and others. The issue of CS2 is a valid one, but not one to be worried about. Adobe has officially said they will not offer universal binary support until CS3, but I can tell you, CS2 works just fine under Rosetta. It will lag on some very specific things for a split second, but overall, you won't even know the difference. as for the license on the software, if you call Adobe, they can sell you an upgrade to Mac version for super duper cheap.
And finally, on your system choice, if you have the cash, GO WITH THE MAC PRO. You can use the monitor(s) you already have, and upgrade at a later date. The Mac Pro excells the iMac in almost everyway possible. The iMac is an amazing machine, but the Mac Pro is a real "pro" tool. It will run CS2 noticeably faster, its infinatly upgradeable as far as HD space, RAM (up to 16 GB of ram), video cards, etc, which the iMac is not. If you can swing it, I would definantly reccomened a Mac Pro. if not, You will be fine with the iMac, its just not as upgradeble in the future. for more information than you could ever possibly need on Macs, check out Mac Rumors
And just a quick aside on Aperture, I would go an play with it at an apple store if you can before you buy it. I tried it out, and found it to be very laggy, cumbersome, and just awkward. this type of software is TOTALLY personal, and the store I went to only had it on laptops, but before you buy, i'd check into Adobe Lightroom, and see what fits your needs better.
Hope I was helpful, and not too wordy