1. Parallels runs significantly faster than Virtual PC mainly because of the change from PowerPC to Intel architecture.
As far as resolution is concerned, you have two options.
One, you can run the entire Windows desktop in a window that sits in front of the Mac desktop. With the latest version of Parallels, there's an option called Coherence that, simply put, allows you to open Windows programs on your Mac desktop. I've tried it and it works like a charm.
Second, you can run Windows in full screen mode, kind of like when you load up a game that takes up the entire screen but Mac OS is still sitting in the back. This works really well if you have a virtual desktop manager installed, such as VirtueDesktops. You can have Windows running full screen on one desktop and Mac running normally on another. When you want to switch, you just hit the shortcut to switch desktops and then you're in a fully functional Windows environment. Plus, the cool factor of switching between OSes is neat.
2. When running Windows via Boot Camp, it's as if you're running Windows on any other machine. It runs full speed without any problems. All the drivers you need are burned onto a CD by Boot Camp, which you install as soon as Windows is setup. Then you can use your machine just how you would use any other laptop, such as a Dell or HP.
3. As far as installing Photoshop on a Windows partition, it would run just as fast as any other laptop with the same specs as a Macbook Pro. So it would obviously run full speed, which can be pretty fast seeing as how the Macbook Pro has really fast parts in it.