HOLLYWOOD: Writing Hollywood spectacles — including X-Men: The Last Stand and Fantastic Four — can be creatively restricting. So writer/director Zak Penn likes to make something unconventional every now and then.

In 2004, he made his feature directing debut with Incident at Loch Ness, a mockumentary starring German filmmaker Werner Herzog as himself and featuring a cast of non-actors playing themselves. The comedy was largely improvised from an outline Penn wrote with Herzog. Afterward, Penn was eager to dive back into the improvisational waters.

''I knew I wanted to make an ensemble improvised comedy, but the question was, where should I set it?'' he recalled.

The answer turned up at a poker game.

Penn is an avowed poker player who plays regularly with actors David Schwimmer, Hank Azaria and Tobey Maguire. Aware of Penn's passion for the game, screenwriter Matt Bierman suggested the World Series of Poker as the backdrop for his comedy.

The stakes are already built into the story, reasoned the filmmaker, so poker it was. And thus the premise for The Grand was born. It's due to open April 4 in theaters across the nation.

Penn and Bierman wrote a 30-page outline involving six main characters, their relationships, scene descriptions and a general direction of where they wanted to take the Las Vegas-set story. From the outset, Penn and Bierman determined The Grand, told documentary-style, would build toward a climactic final tournament. The actual winner of the tournament would be left to fate.

Poker is popular in Hollywood and there was no shortage of actors willing to sign on to Penn's mockumentary, which is reminiscent of Christopher Guest spoofs like Waiting for Guffman and Best in Show.

''I literally begged Zak to let me be a part of it,'' said Cheryl Hines, an avid poker player who stars in the HBO comedy series Curb Your Enthusiasm.

Initially, Ben Affleck was going to play Harold, a mathematical genius/poker whiz with Asperger's syndrome. Friends star Schwimmer was going to have a role in the comedy as well. But owing to scheduling conflicts, neither made it into The Grand.

Former SNL star Chris Parnell stepped in for Affleck, and Woody Harrelson, Ray Romano, David Cross, Richard Kind and Dennis Farina also joined the cast (along with a host of Hollywood cameos). Herzog also appears as a high-stakes German player with a penchant for hurting animals.

''He got that it was just a joke,'' assured Penn. ''I don't think he harbors any ill will toward animals. The bunny really liked him.''

The actors, many of whom are seasoned stand-up comedians, relished the opportunity to improvise in a feature film.

''When we would shoot something, we would kind of have an idea . . . but even that wasn't always for sure,'' recalled Parnell, who wrote much of his own dialogue.

''My character wasn't really written at all,'' added Romano, who plays Hines' self-centered, stay-at-home husband. ''We had to come up with these quirky little things — like the fact that he's a fan of online fantasy football.''

Hines, Romano and some of the others have played in celebrity poker tournaments, so they were well acquainted with the game. (Hines won $50,000 at an event.)

For Farina, a Chicago cop turned actor, improvised comedy was new but appealing. ''I enjoyed it,'' said the former Law and Order star, who plays a tough-guy named Deuce. ''I'm not a comedian, but it was a lot of fun.''

All of the actors were up for the unscripted final tournament, but Penn started to get cold feet during production at the storied Golden Nugget casino.

''I completely panicked,'' he recalled with a laugh. ''We got there and I said, 'This is asinine. I can't do this to myself.' ''

He worried that the final round of the tournament would be impossible to film and might not fit the story.

''One of the reasons you don't leave the outcome of your story to chance is that you have no idea what comes afterward,'' he said. ''It's not like the story simply ends after the final card is dealt. There needs to be scenes of victory, defeat and tying up subplots.''

Penn talked it over with Andy Newman, the film's poker adviser, who assured him it would be more difficult to ''fix'' a poker tournament than to leave it to chance. So the actors played a real game.

Penn admits he wouldn't have written the outcome the way it happens, but he likes the result nevertheless. Still, he had to make contingencies for various tournament outcomes — so he shot 12 different endings. (The alternate endings will likely appear on the DVD version of The Grand.)

Harrelson, who plays a womanizing alcoholic named One-Eyed Jack Faro, says shooting the final game sequence was almost as intense as playing the real thing.

''It's really a drug of sort,'' he said of poker. ''It gets you all jacked up and your adrenaline pumping. I've had a lot of very intense poker moments.''