02/22/2008 at 08:05 AM EST
just signed on to star in her first feature film, she confirms to PEOPLE – and boyfriend Nick Lachey
is there to support her every step of the way.
"I just got the phone call this morning," she said of signing on to the movie, called Redefining Love
. "I'm like Nick, honey, how did this happen?"
The former MTV host kept mum on the plot, only saying that the role has a "great character arc." "I just hope I can portray this character as the writers had hoped," she admitted at Reebok's Freestyle World Tour campaign launch party in N.Y.C. Thursday. "I'm nervous as heck!"
Luckily, the 34-year-old Lachey – Minnillo's boyfriend of almost two years – is there to help soothe her nerves. "He's very supportive and very calming," the 27-year-old said. "He's one of my biggest cheerleaders."
Just don't expect the former 98 Degrees star – who has guest-starred on Charmed
and Hope & Faith
– to offer up any acting tips.
"He's not helping me [run lines]," she said. "I can't. It's too embarrassing to try it with him. It's too nerve wracking. I start to giggle with him and I can't take him seriously. It's just one big mess!"
The former Miss Teen USA begins filming this April in North Carolina.