Like the family cat, presidential elections, or even significant others, computers can be extraordinarily fickle. One moment, they're happily ferrying your email, spell-checking your paper, and accompanying you toexotic Web sites without the slightest peep. But the minute you change the slightest setting or do anything out of the norm, they'll hiccup and throw a fit. The fact of the matter is that a computer can give you all sorts of headaches if you don't know what you're up against.