I disagree a total novice will think he is invincible,
stat them off with WinXP and a good security suite, teach them early.
Other clients more correctly think of the computer like a car. While they don't exactly know how it works, they realize there is maintenance involved and a general understanding of its operation will make for a better experience. These guys can use either Macs or Windows, but Windows is generally preferred.
Taking the car analogy further, a Linux user is a guy who likes to get under the hood and add after-market parts. Not a bad thing, but not everyone is like that.