The "it" boy of crude comedy, Seth Rogen, loses some of his comic heat when he teams up with the guy who invented the genre, Kevin Smith, in "Zack and Miri Make a Porno."

It's a raunchy R-rated farce (appealed from an NC-17) in the standard Smith style — comical sex talk with the women just as dirty as the guys, dated pop culture references, a big gross-out moment and an endless litany of oral sex jokes.

But it's a slow-footed film that confirms that Smith may never be able to lift his game to that "40-Year-Old Virgin" level of heart and romance. He's just too juvenile to pull it off.

Art imitates porn in this dully shot and edited comedy about a couple of desperate platonic roommates (Rogen and Elizabeth Banks) who decide to do a cheap porno together to make the rent. When Zack jokes that their high school classmates are one target audience, and doing a spoof of "Star Wars" will give them another, he's breaking down Smith's marketing scheme. Put "porno" in the title and "Star Wars" in the plot and the Smithheads will come.

Zack cons a colleague from the coffee shop where he works (Craig Robinson of "Pineapple Express") to put up the money. And he sweet-talks the too-hot-but-still-single roomie into being his co-star.

"Miriam Linkey, will you have sex with me, on camera?"

They cast the picture, giving roles to Bubbles (porn actress Traci Lords, showing some mileage) and Lester (Smith's pal, Jason Mewes, looking like death). A hockey pal of Zack's (Jeff Anderson, another Smith mainstay) will run camera.

Disasters that befall a lower-than-low-budget "film" hit them. But they improvise, adjust, and it's lights, camera, copulation! Other crude couplings are just time-killers until the main event, Zack and Miri's big scene. Since they've been friends since first grade, that promises to be awkward, if they ever get around to it.

Banks is the heart of this, and if there are any "feelings" that get in the way of Zack and Miri's porn plans, she makes them believable. But as with every Rogen leading lady, you could scratch your head bald puzzling over what she could possibly see in him. Miri is clumsy, making bad life and career choices. And Zack? He's so thinly written that he's basically a plot device.

Justin Long improvises a frat boy's idea of a gay porn star and amuses. A loud, profane Tisha Martin Campbell's rant near the finale is the funniest scene in the movie.

The aging Smith film vets in the cast remind us that Smith and Co. are older and that like the "Dumb & Dumber" Farrelly Brothers, Smith has lost his fastball and is scrambling to adjust to life in the post-Judd Apatow comedy universe.

But it's not enough to simply steal Apatow actors (Rogen, Banks and Robinson). "Zack and Miri Make a Porno" is just the aging dead-end kids from "Clerks" finally getting the gumption to go out and do something with their dirty, limited little minds — and videotape it.