Molly Shannon’s popular Saturday Night Live character has moved up to the big screen. In the movie “Superstar” that opens Friday, the Irish-Catholic, overly-nervous teenager, Mary Katherine Gallagher, has a chance at being an extra in a Hollywood movie with positive moral values if she wins her school’s talent contest. It seems the perfect plan to finally get the long-awaited kiss she dreams about that only movie stars get.Mary Katherine’s obsession with a popular and great dancer who goes to her school, Sky (SNL’s Will Ferrell), her clumsy actions and precise dance moves, and the movie quotes embedded into her mind from being a video store’s rewinder girl fill the movie with endless laughs. Changing from short and sweet skits to a movie-length feature has just drawn out the laughter of Mary Katherine.Though the writer, Steven Koren, former writer/producer of “Seinfeld,” successfully kept the humor kicking, Shannon said she recognized the difference in moving from skits to a movie.”With the skits, you have to tell the story really quickly–establish what the character wants really quickly and do jokes faster. With the movie, it was a little more precise. You have got to take more time,” she said.Shannon was the person who created Mary Katherine Gallagher while attending New York University in the 80s. The character isn’t so far from the star’s own personality. Shannon herself was raised in an Irish-Catholic home. “I have always been pretty nervous myself,” she said. “I really truly get nervous to perform and feel this intense feeling and I think that (the idea of Mary Katherine) comes from that.”Different from the skits, Shannon does not fall, trip and hurt herself (although she does throw some punches) as much in the movie. “It (falling so much) is sort of hard after awhile, hard on your body. Sometimes it hurts,” Shannon said with a laugh.Another trademark of Mary Katherine is the frequent display of her underwear. “That sort of happened by accident,” said Shannon. “The first time I did the character with Gabriel Burn, there was a joke that we had in the sketch where I was singing a song and I put my leg on a stool and my underpants would just show. Between dress and air (time) Lorne Michaels said, ‘Maybe you should make your skirt a little higher–make sure you see the underwear during the joke.’ So that was actually Lorne’s idea and then it just kept being that you had to show the underwear.”Since Mary Katherine fantasizes about getting a sensuous, dreamy kiss, she prepares herself for the moment by practicing–on things such as trees and stop signs–during the movie. “I tried to play it truthfully,” she said. “Will (Ferrell) and I always say this thing that you have to play the real moment–just to play the scene truthfully, not act like you’re doing comedy. Play it like you’re really doing an intimate scene with somebody.”Shannon said working with director Bruce McCulloch was great. “He’s from ‘Kids in the Hall.’ He used to be a performer himself so he was really great to work with. He’s really into style…and he would know when to let you keep going because he’s a performer himself. It’s great when directors are actors because they know how to work with actors better than just directors that just direct.” In the past, Shannon has played Mary Katherine with many big names on SNL. “I loved doing it with Tina Turner,” said Shannon. “(And with) Steven Tyler from Aerosmith–that was pretty amazing. I’d love to do it with Courtney Love–that would be great. I like her. She can be mean and she doesn’t care what people think of her. I like that. I’m always too Catholic and too concerned about pleasing everybody.”Shannon is currently working on her next movie, “How the Grinch Stole Christmas,” with Jim Carey. “People think comedians are all wild all the time. He’s (Jim Carey) very serious. He approaches comedy very seriously.”As for the future after the “Grinch,” Molly said, “I’d really like to get into doing movies and just work with good writers and just people that I like. It’s nice when you’re with people that make you laugh. I don’t mind continuing to do television because I love television. Just to keep working. I’m so grateful to be making my living acting. If I could keep doing that, that would make me happy.””Superstar” hits theaters Oct. 8.