Anna Faris, Katharine McPhee, Rumer Willis and Emma Stone, stars of 'The House Bunny,' releasing August 22, stepped out in NYC Monday night for a CosmoGirl-hosted party and screening of their new comedy -- and ET was with them for the exclusive sit-down interview!

What did it take for headliner Anna to get into Playboy bunny shape? Which behind-the-scenes moments during filming did the fab foursome find funniest? And did any catfights erupt on the set? Click our video to find out! And be sure to check out the current issue of CosmoGirl, on sale now.

"We all sort of naturally fell into the roles that we played," Anna tells ET. "I felt definitely like the house mom at times. I had to crack the whip!"

In 'The House Bunny,' Anna plays Shelley Darlington, a Playboy Playmate who is kicked out of the Playboy mansion because she's "too old" at the age of 27. Homeless and without a job, she moves in with the brainy college girls of Zeta Alpha Zeta and learns a thing or two about individuality and heart -- while they get a few tips on how to amp up their sex appeal and land the guys!

And on the subject of landing a big role, Rumer tells us: "It's a big difference from being you know -- watching as kind of a side viewer when I was a kid, to now be the one that people are kind of all afuss about."

The film also stars Colin Hanks and Beverly D'Angelo.