There are two main differences between a Macintosh and a Windows based PC. The first in hardware and software related and the other is about market share and malware. I will discuss the hardware/software issue first as it is really the major difference. First, the real difference is that the Windows OS uses what is called the Registry. This is the heart of the OS and it stores every single feature and command for both the OS and the applications installed on top of the OS, as well as every driver for the hardware to "talk" with the software.
The registry is critical to proper system, program, and hardware functionality. If anything goes wrong with the registry it can cause anything from a fatal crash to all sorts of annoying to serious issues with the OS and programs, hardware. For example, if a single registry entry becomes corrupt, depending on what the entry is related to, lets say the cammand to start iTunes, iTunes will not be able to start. It could be something more serious such as icons missing, features missing or not responding correctly, your keyboard could malfunction, and the list goes on forever. Every program and feature is inside the registry, so you can see how sensitive it is to errors. When you install a program it is entered into the registry, that is where the commands for every single feature is stored. When you want to remove a program often registry keys are left behind. The more programs you install and remove the more registry "bloat" you get in the system. While there ARE so called "registry cleaners" these types of tools are actually bad for the system. You can never tell when they remove a valid and vital key, and when this occurs the issues may not show up right away but eventually they do and all sorts of odd issues will begin to occur, without rhyme or reason.
Another issue with Windows based PCs is that the systems which are built for you and which come with the OS pre-installed are stuffed with useless trial or "free" programs, with the worst of the bunch being either Norton or McAfee security suite. Security suites must embed deeply into the OS, and if you want to use a different vendor you MUST fully and completely remove the one which is installed, which is nearly impossible and when it seems removed it really is not. Then you install another vendors product and all sorts of issues occur. They can begin right away or wait for a trigger event and can actually cause a fatal crash.
The Apple Macintosh does not utilize a registry so it is far more stable than a Windows based PC. As for the second issue, security, the Mac is just as prone to viruses or other malware as Windows. It is just as prone to being remotely taken over. The only reason the Mac appears more secure is because it has such a small market share. Malware writers tend to write for the largest market share. This is because the code they write will work on a larger number of machines. But, don't let anyone tell you that a Mac is more secure because of the way it is built, that isn't true.
Don't get me wrong here, Windows has a real good place in the market. Windows opened up more people to access the Internet and use systems than any other OS. It is made cheaply and that was passed on to consumers. This is why it has been so popular, and spread across the world so quickly. Microsoft went for the fast nickles instead of slow dimes. Bill Gates made billions while placing more computers in businesses, hospitals, government, and homes than any other company.
If you can afford a Mac, and have the hardware to support it then go with the Mac. The Mac is a far more solid machine and will last a long time. This is not to say that with the appropriate care a Windows based system will not also last a very long time. By only installing the software you are positive you will use, and keeping away from the stuff you are interested in, but never use once installed, by not removing software once it IS installed, staying away from known malware websites, and keeping the system up to date with updates and driver updates and using a solid security system Windows can and will last as long as a Mac. The problem is that most people do not know how to take care of their system. So, if you like the Mac and can afford it by all means buy one, but be sure to install a security system, at the very least an anti-virus.