First, lets look at the operating systems. Microsoft's operating system is called windows. Apple's latest operating system is called Leopard. Microsoft's operating system is currently the dominant operating system in the market today. Apple's Computers have a higher price tag than Microsoft's but they tend to last twice as long and have a lot more cultural appeal. Microsoft's computers are typically used for entry level tasks such as web browsing or writing papers. Apple's computers are typically used for more advanced tasks such as video/picture editing, music production, or graphic design.
All in all they both make a great machine. It all comes down to what type of tasks you encounter in your daily life and also what your personal preference is. In my opinion, Apple is the way to go simply because of the longevity of the computer. I also enjoy the layout of the operating system.