"Disinterested" and "uninterested" have different meanings, but people are starting to confuse them. Grammar Girl has a trick for getting them right.
An uninterested person is bored, unconcerned, or indifferent; a disinterested person is impartial, unbiased, or has no stake in the outcome. If you're on trial, you want a disinterested judge. Unless you're a lawyer, the word you're generally looking for is "uninterested," but a quick news search shows that "disinterested" is frequently misused by the media. Here's how to use them properly:
Squiggly couldn't help yawning; he was uninterested in fishing stories.
The ex-wife can hardly be considered a disinterested party.
Bryan Garner, author of Garner's Modern American Usage, states that many people have given up the fight to preserve the distinction between the two words, but he believes it is worth preserving. The Merriam-Webster's Dictionary of English Usage writers note that their research shows "disinterested" taking on the additional meaning of "uninterested," but "uninterested" being used to mean "disinterested" only rarely (and in fact, being used less often in general than "disinterested").
Get more tips like this in The Grammar Devotional: