Recap:
Windows PC: can buy all sorts of different kit from different places, and the greater range of processors etc. means that you can get a cheaper computer. Runs Windows with all sorts of security holes so you need anti-virus. Far more popular so easier to buy software for it, and easier to get support from friends. Tends to still look like something you'd want upstairs out of the way, and not in the limelight anywhere. Due to increase in software, it's easier to find free little pieces of software that you want from a google search.
Apple Mac: made to Apple's specifications, and they want more powerful computers. So they're more expensive than the cheaper windows-based machines, simply because they're higher-end machines. Runs Mac OS X that is technically superior to Windows. Less people have them, so less software available for it. However, still plenty available that will let you get done whatever you want to do, with the exception of the games industry and some specific software like certain accounting packages etc. Better interface, easier to use. Better design. Because everything is integrated by Apple you get a better all-round experience, so people often say that things 'just work' on it. Example: wireless cards. On windows if you buy a wireless dongle for your laptop or use the built-in one, the interface can be different to the one that your friend has on his Windows machine. Etc. On a mac, which has had built-in wireless since about 2001, the interface is always the same. Everywhere. Far simpler.
Case in point: lots and lots of professional admins used to use GNU/Linux on their laptops to get stuff done, because from a technical standpoint they were more stable and 'better' than windows. Once Mac OS X came to force, many swapped over. You always hear stories about people going from Windows to Mac. But never the other way round. I wonder why?