''American Pie'' sexpot shines on TV --''Buffy'' favorite Alyson Hannigan brings her redhead act to ''How I Met Your Mother''

Tired of a certain well-trod sentence involving a summertime destination and a woodwind instrument, American Pie star Alyson Hannigan is in the market for a new catchphrase. Despite her role as Lily, a libidinous kindergarten teacher, on CBS’ new sitcom How I Met Your Mother — and the fact that it’s been six years since one time, at band camp, she dallied with a flute — fans still holler ”BAND CAMP!!” at her in the street. But now the 31-year-old redhead comes prepared. ”I just say, ‘If I had a nickel for every… Oh, wait. I do.’ Haw haw haaaaw!” guffaws Hannigan. ”It helps in those awkward situations when you’re like, People. Really…not now. Please.”

It also helps to have something good goin’ on, and How I Met Your Mother — an ensemble comedy starring Josh Radnor and Neil Patrick Harris, about a hapless twentysomething’s search for love — has averaged 10.6 million viewers weekly. CBS is so pleased with Mother that it recently picked it up for a full season. ”We wanted Lily to be strong and in charge, but because it’s Alyson, that strength and maturity never comes off as shrill or too harsh because you just love her instantly,” says exec producer Craig Thomas. ”She’s got that big-ass smile,” adds Joss Whedon, creator of Hannigan’s breakout series, Buffy the Vampire Slayer, who, admittedly, is a biased party — Hannigan and her husband, Alexis Denisof (Wesley on Angel), are godparents to Whedon’s son. ”And those I-stepped-out-of-a-Disney-cartoon eyes. And then a mouth like a sailor. She’s an extraordinary woman.”

Hannigan’s career actually started out pretty ordinary, with McDonald’s commercials in her native Georgia at age 4. She moved to L.A. at 11, and after a string of random gigs (including the 1988 film My Stepmother Is an Alien), she landed the role of Willow, the wallflower-turned-Wiccan lesbian, on Buffy in 1997. After the show wrapped in 2003, she scored a development deal at NBC (it went nowhere), then a role opposite Luke Perry in a 2004 London stage production of When Harry Met Sally (”I had a crush on him back in the day, but that goes away once you’re working together. You’re like, ‘Oh. You’re shorter than I thought you’d be”’). Last January, she came back to TV for a doomed ABC pilot starring Jennifer Love Hewitt. ”That was a matter of signing on before there was a script,” she says, ”which is a stupid thing to do.”

Free of her ABC contract, Hannigan found her way to Mother‘s Lily. Talking about her new character, the actress wears a big gloopy smile, until you point out that once again, she’s playing a horndog (see the Pie trilogy). ”So not intentional at all,” she exclaims. ”I think they like the contrast of hearing ridiculous things coming out of my sweet little face. It’s like, ‘Aw, look!”’

Back on the big screen, Hannigan just finished shooting the lead in Date Movie, a romantic-comedy spoof from Aaron Seltzer and Jason Friedberg (Scary Movie). ”We’d say, ‘We’re not gonna let you get sprayed in the face with hummus because it could blind you,”’ says Seltzer, ”and she’d say, ‘No, you have to shoot me in the face.’ That was really admirable.” But slapstick comes easy; what Hannigan needs is the big dramatic role that finally puts band camp behind her. ”I want to work with Jim Carrey in his artsy movies,” Hannigan suggests. Nothing’s in the works yet, but she has taken one important step down the maturity path by kicking her ”sailor mouth” tendencies. ”Those were my younger years, and I’ve cleaned up,” Hannigan admits. ”Many of my friends have children, so I’ve curbed the cursing. It’s a whole new mouth!”