Tom & Dick each buy notebook computers.
Tom gets a MacBook. He used Leopard for awhile. 3 months down the road, he uses Bootcamp & Vista Home Premium, or Parallels & Windows XP (with SP2).
Dick gets a Dell.
Now, you've probably got a better idea than I do about what extra hardware spec.s Dick got, if any.
But a year after purchase, Tom's working with Leopard & VISTA, and can choose to use both or one or the other.
Dick is stuck with VISTA Home Premium. (I'm not counting Linux; some do, obviously).
When you buy a Mac, you buy into the option of the Mac experience, while retaining the option (for the cost of the Windows OS (hit newegg.com & aim for OEM/System Builder versions, I believe, to save a lot of money) & maybe Parallels) to have the Windows experience.
When you buy a PC, well, unless you're a Linux sort, you get Windows. Period.
I've historically found that Macs feel more 'organic,' and Windows more like a tool box. Like comparing a home to a house; lot of similarity in function & appearance, but the difference is there.
Richard.