There are three flavors of musical biopics.

One type ends with a plane crash (to contrast the mortality of man with the immortality of song). The second ends with a drug overdose (to slam home the moral of how creation and destruction are flip sides of the LP of life). The third ends with a post-rehab career rebound (all the better to applaud the unkillable artistic spirit).

The clump of cinematic silly putty called Walk Hard: The Dewey Cox Story, spoofs the conventions of all three as it follows its musical shape-shifter (John C. Reilly) from rockabilly goat to folkie troubadour to rock dinosaur.

While it might not have the laughs-per-minute ratio of the Naked Gun movies (but then, what does?), it is a reliable titter generator for boomers and their echo boomlings.

Like a musical Zelig or Forrest Gump, Dewey Cox (whose surname is stroked for every naughty pun imaginable) for five decades is at the center of the hurricane that is pop music, mastering every idiom from rock to rap.

As a boy, Dewey loses his musically gifted older brother in a freak accident that inspires his father's grumpy refrain, "The wrong kid died." Which in turn inspires Dewey, the living, less-loved child, to prove himself to Pop.

Dewey starts out as a heartbeat-skipping teen crooner, goes rockabilly and feels a whole lotta shaking going on, then, like a rolling stone, morphs into a protest poet. He radiates bad vibrations as a reclusive pop guru, loses his way in an octopus' garden when he goes psychedelic and finds his heart of gold when he gets inducted into the Rock and Roll Hall of Fame.

Which is another way of saying that Dewey Cox plays like a Sonny and Cher Comedy Hour skit extended to feature length, a parade of shaggy wigs and shagalicious fashions.

Written by Jake Kasdan and Judd Apatow, evidently after two too many viewings of Walk the Line, the film offers puckish Reilly, who rode shotgun in Talladega Nights and Chicago, an opportunity to drive his own vehicle.

Reilly is recklessly funny. But Dewey is a better showcase for toupees and trousers than for his singular talents.

Jenna Fischer scores smiles as Darlene, the puritanical hottie who sings backup for Dewey. Likewise, Tim Meadows as Dewey's drummer, ever ahead of the curve when it comes to the happening drug of the moment.

Big laughs? More like big smiles. Most of which rely on a knowledge of rock history.

As a tousle-haired troubadour of the Dylan school, Dewey fulminates something to the effect of, "My sense of taste is wasted on the phosphorous and orange peels of San Francisco's ax-encrusted frenzy. So let me touch you."

As a bearded-whale mad genius of the Brian Wilson stripe, Dewey snaps, "Open your mind and learn to play the effing theremin!"

I will, Dewey, if you open your heart and let John C. Reilly out.

Walk Hard: The Dewey Cox Story **1/2 (out of four stars)

Directed by Jake Kasdan. With John C. Reilly, Jenna Fischer, Tim Meadows, and Kristen Wiig. Distributed by Columbia Pictures.

Running time: 1 hour, 36 mins.

Parent's guide: R (full frontal nudity, sex, double entendres and drugs galore)

Playing at: area theatersEndText