Y'know, like "Nightline." In September, with correspondent Robert Krulwich mustering an air of only slightly feigned guilelessness on the mic, MC Ted Koppel's show conducted a painstaking three-night investigation of hip-hop culture, eventually concluding that it makes some very nice bank for a great many people, and (thus) is definitely important, if a little scary and irresponsible.

Then there's Newsweek, which got out the extra-extra-broad brush for the recent cover package, "Battle for the Soul of Hip-Hop," about how today's rap is so violent, misogynistic and materialistic that even some rappers find it troubling. The "Battle" was a celebrity death match pitting Mos Def -- fast becoming hip-hop's most vocal neoconservative -- against Eminem, enemy of all that is good, and Cash Money's iced-down Millionaires. The subtext, roughly, was that because the music reaches a wide, eager and young audience that rock can only dream about, hip-hop's problems are everybody's problems. Also, "booty videos" are bad. Oh, so bad.

The Brooklyn Museum, which stared down both the Catholic archdiocese and New York Mayor Rudy Giuliani last fall when both attacked its controversy-courting "Sensation" art show, probably doesn't care what a few media naysayers have to say about hip-hop. Besides, the museum's new hip-hop exhibit, "Hip-Hop Nation: Roots, Rhymes and Rage," crams over 400 rap artifacts into four rather cramped ground-floor galleries, which leaves little room for dung paintings. A roughly chronological survey of rap's journey from Bronx block parties to cold-lampin'-in-the-Hamptons, "Hip-Hop Nation" was originally staged in November 1999 at the Rock and Roll Hall of Fame in Cleveland.

For its Brooklyn debut, the museum's Kevin Stayton and guest curator Kevin Powell (former Vibe scribe and "Real World" cast member, and card-carrying Gen Rap pundit) have beefed up the show with supplementary East Coast content. They've also solicited the input of a large and varied advisory committee, which includes both old-school faculty members (graffiti artist Lady Pink, early rap impresario Fab 5 Freddy) and industry machers (Russell Simmons, Jann Wenner.) All this effort puts the exhibit in sort of a weird position. It's a frustrating failure, but it's a painstakingly researched, authoritative failure. Ultimately, the worst thing about it is how close to good it comes.

Hip-hop's prehistory offers a team of curators any number of potential entry points: African griots and other oral poetic traditions, the Beats, talking blues, Muhammad Ali trash-talk, C.W. McCall's "Convoy." But "Hip-Hop Nation" begins with the basics, and in the relatively recent past. A yellow Cab Calloway zoot suit is displayed front and center, signifying the visual pomp and verbal hi-de-ho hip-hop picked up from jazz. Vinyl LPs -- Vicki Sue Robinson, Dizzy Gillespie, the Last Poets -- highlight the genre's debt to the soul and funk in Mom and Dad's record collection, the main factor that kept rap from making generational division a priority to the extent that rock always did (at least until Bob Dylan's kid started making Tom Petty records).

From there, it's on to the break of hip-hop's dawn: With its roots established, hip-hop bloomed across the poverty-scarred South Bronx in the late '70s and early '80s. The exhibit illustrates this phase, the music's teen years, with a collection of vintage rap-show flyers that's almost worth the suggested donation on its own. The T-Connection club's groovy art-deco handbills (one Afrika Bambaataa/Jazzy Jay/Treacherous 3 triple bill is "dedicated to disillusioned folks") share space with posters for community events that just happened to include hip-hop (the Cold Crush Brothers playing a graduation ball at Throgs Neck Community Center in the Bronx in 1982, and something called the "1979 Tennis & Terry Cloth Affair," presented by the P.A.L. Teen Council) and party invites that approximate the design sensibility of garage-sale announcements. By pointing out hip-hop's unassuming beginnings, this stuff testifies, succinctly, to the form's extraordinary, who-woulda-thunk-it growth. Puffy sells out Madison Square Garden now, but there was a time when the phrase "hip-hop show" meant Kurtis Blow doing a playground-renovation benefit at the skating rink around the corner. ("Parents relax downstairs in lounge, while your child skates upstairs.")

When it left the outer boroughs en route to the world stage, though, hip-hop got complicated real fast. In 1982, when Charlie Ahearn and Fab 5 Freddy shot the lo-fi quasi-documentary "Wild Style" on the streets of the Bronx, they assumed they were catching a fad on its way out; four years later, Rick Rubin-produced, Russell Simmons-masterminded juggernauts like Run-D.M.C.'s "Raising Hell" and (especially) the Beastie Boys' "Licensed to Ill" were sounding like rock and selling like pop. There's a shift in tone here, and the museum kinda turns into the Hard Rap Cafe, as hip-hop stars -- and their significant-by-association hip-hop stuff -- take over the conversation. Which is, in its own way, perfectly fine -- for any self-respecting rap geek, the chance to view Afrika Bambaataa's space-shaman cloak and Boogaloo Shrimp's dance pants, Slick Rick's eye patch and Rakim's Dapper Dan Gucci jacket (as seen on the cover of the Eric B and Rakim classic, "Follow the Leader"), Flavor Flav's timepiece and (icon of icons) Run D.M.C.'s Adidas, is akin to gaining admission to the Batcave trophy room where Bruce Wayne kept the giant penny.

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