The first scene in "Dazed and Confused" shows a souped-up muscle car creeping around the corner and into the frame.

Decent enough all by itself. But playing behind the scene is the instrumental opening of Aerosmith's "Sweet Emotion," a song with so much swagger it practically leaps out of the speakers, grabs you by the collar and screams, "LISTEN TO ME!"

Used to open Richard Linklater's 1993 film about the last day of school at a Texas high school in 1976, it has a similar effect on the audience, announcing that this is going to be one cool movie before it's even started.

In other words, it's perfect.

Music is crucial to movies and has been since they started using sound (and even before, with a piano player accompanying the silent on-screen action). In the hands of a less-confident filmmaker, it can be used as a crutch, a shortcut to emotion that the writing, the acting or both can't convey. That results in something less than a movie, more like a bad music video.

But used correctly, music enhances a film, helping to set a tone or accentuate a mood.

In Greg Mottola's "Adventureland," for instance, before we see anything we hear the biting, angular guitar of the Replacements' "Bastards of Young." And immediately we are transported to the mid-'80s, Paul Westerberg exclaiming, "We are the sons of no one," capturing the alienation of an age that Mottola's movie will go on to explore in depth.

Of course, some movies are inseparable from their soundtracks. The best example, and the best soundtrack ever, is "A Hard Day's Night."

The music is central to everything around it, yet the film also captures the zany reality of Beatlemania for John, Paul, George and Ringo. "Purple Rain" is a similar experience. Prince's songs are great, and the film couldn't exist without them.

It's not surprising that the music used in Cameron Crowe's films is important; he's a former writer for Rolling Stone and is married to Heart's Nancy Wilson. John Cusack holding a boom box over his head playing Peter Gabriel's "In Your Eyes" in "Say Anything" has become an iconic image for those of a certain age, and the band singing along to Elton John's "Tiny Dancer" in "Almost Famous" is unexpectedly moving.

Indeed, a single song often will do the trick. Perhaps nowhere is this more explicit than in "Garden State," which Zach Braff wrote, directed and stars in.

He comes upon Natalie Portman wearing headphones in a doctor's office. He asks what she's listening to, so she offers them to Braff and says, "You've got to hear this one song, it'll change your life, I swear."

Sure enough, he hears "New Slang" by the Shins, the band's ode to disaffection, and the mood of the film and, especially, the makeup of Portman's character is instantly heightened, clarified, explained. It's a great, and useful, moment.

It may not really change your life. But it certainly changes the movie, for the better, as does any song used the right way.

So crank it up and enjoy.