Meh. I have a Mac, but I run Windows, Mac, and Linux on it. I'm indifferent as to which one is best, although I spend most time in Linux, I 'spose. In general, I think, Mac OS X is easier to keep running well than is Windows Vista, but I personally don't mind dealing with either.
The general difference for a casual user is the operating system. This is the basic computer program, essentially, that controls the fundamental aspects of how your computer runs (well, slightly above BIOS or EFI, but that's another issue). The appearence of Mac and Windows will be somewhat different, but they have their similarities. The main difference is that Windows programs cannot run on Mac OS X, and visa-versa. The reason for this is because of the libraries, mainly. Computer programs are coded to do many different tedious tasks over and over again. Instead of re-writing the code over and over again for those basic tasks, a programmer will call a function in a library... essentially, it opens a book and looks up how to do something, so that the programmer doesn't have to type those instructions over and over again. Windows and Mac have completely different code libraries, or instruction manuals, so to say.
However, some programs work on both Mac and Windows (and typically Linux), such as Firefox. I highly recommend running Firefox or Opera on any computer.
