You might think that "Shopgirl," a romantic comedy starring perfectly paired couple Claire Danes and Jason Schwartzman and written by comedic legend Steve Martin, would be a must-have item. Based on Martin's critically praised 2000 novella, the story of a beautiful Beverly Hills clerk would seem to sell itself: Martin's sarcastic wit fits audiences as snugly as a pair of worn slippers, with Danes' dry line deliveries smooth as a pressed shirt and Schwartzman as guilty a pleasure as any frivolous shoe-store purchase. Before the finished outfit could be assembled, however, a lot of time had to be spent in the dressing room.

"I was in anxiety before I met [Martin]," admitted director Anand Tucker, who took on the difficult task of directing a movie alongside its all-powerful writer, star and creator. "He said, 'Look, I want you to make this movie your way, otherwise I'm not gonna be any good.' He has a history of collaborating with directors [like] Mick Jackson on 'L.A. Story,' and he's very good at [collaborating], and he really knows when to come in, and when to step back."

"It was tricky. I was nervous," former "Rushmore" whiz kid Schwartzman said of his writer and co-star. "Steve Martin's so dope."

The actor and former Phantom Planet drummer was doubly panicky when he took on what was much more than simply his most dramatic starring role to date: He was also playing a character clearly based on Martin's interpretation of himself as a young man.

"It eventually appeared to be me, cinematically," Martin said of Jeremy, the funny-but-unlucky drifter who offers what little he has to Mirabelle, played by Danes. "When I was writing it I was actually an author, you know, writing a book. ... But there certainly is a difference in energy between a younger man and an older man."

That irreverent energy is about all Jeremy has to his advantage over Ray Porter (Martin), a relentlessly smooth millionaire who hopes to woo Mirabelle himself with champagne wishes and caviar dreams. "Both of our characters are striving for the same thing, it's just that we each are further along in areas that the other isn't," Schwartzman remembered of the contrasting Casanovas. "He definitely has the suit figured out, and the suaveness, and the platinum credit card and smooth leather boots. My character doesn't know what to say and is awkward, but I think my character is also really sincere and really willing to lay it on the line and really love this person."

So while Schwartzman the thespian was trying to grow up, and Martin the writer was trying to grow down, Danes was caught in the middle. To make matters more difficult, she was stepping into a character whose financial desperation had already been oddly branded by Winona Ryder's bizarre 2001 shoplifting arrest (Ryder claimed to be doing research for the part).

"Money is only irrelevant if you have it," Danes said of one of the film's deeper subtexts, which has the two twentysomethings saving pennies while constantly surrounded by wealth. "When you don't [have money], it really defines your experience.

When she initially read the script, Danes was amazed that Martin, a 30-year show-business veteran, could so clearly recall the particulars of his salad days. "Steve was great in establishing those details," Danes marveled. "He's really exact, even with the numbers. We learned how much [Mirabelle] owes, exactly, and what she has to pay off, and you know she has $4 every day to buy her sandwich. This seemingly petty stuff can really impact a person's experience."

The most daring decision to be made with "Shopgirl," however, wasn't Schwartzman's casting or Martin's attempt to star and write without directing. It was, instead, his third on-the-set job.

"I do the narration in a different person, we'll call it, than I play in the movie," the comedian/dramatist recounted.

"It wasn't an easy decision, but I think it was one of the right ones," Tucker insisted about the highly irregular decision to have an actor play a character and simultaneously voice a completely unrelated, omnipresent narrator.

"We did actually talk about the narration thing, because, you know, it's a complex thing, isn't it? Who should be the voice of that narrator?" the director asked. "I did go back and forth for a while, and then eventually I thought, 'Well, you know what? It has to be Steve, because the novel was written by him.' This is a piece that comes from Steve's DNA, and I think audiences are sophisticated enough to understand the different levels at which the story's being told. And there are some aspects, I think, where I find it very moving. It's Steve commenting on the character he's playing."

"That's a device," Martin said of his unusual selection as narrator. "I like to think about it as a little bit of a mystery ... the director describes it as a statement of authorship. It's kind of a sophisticated concept, but I like to think of it almost as my character looking back intellectually, but not at an advanced age."

"He just nailed it," Schwartzman said of the finished product, on sale now for your shopping pleasure, at movie theaters nationwide. "I don't know how he nailed it; that's why he's Steve Martin ... he's a scientist of the heart, or something."

Check out everything we've got on "Shopgirl."

Visit [article id="1488131"]Movies on MTV.com[/article] for more from Hollywood, including news, interviews, trailers and more.