Macs are PCs. There's no difference. The only thing is that Apple make both hardware and software, unlike Microsoft, Dell etc. Hence they create one complete package, and don't have to worry about as many driver issues etc. as Microsoft does, so their software tends to run smoother out of the box. It's also now got a more solid foundation, in the shape of freeBSD, than Windows has.
They'll be with Intel for a good while longer. At least 10 years.
The Gx processors were good, but they consumed too much power and gave off far too much heat. Since Apple wanted to create faster portables, they needed a processor design that beat the G4. The G5 would never fit into a laptop without it overheating all the time, and hence they switched to Intel, which has a roadmap including many processors specifically designed for mobile platforms.