Rain only helped add to the British atmosphere surrounding this week's New York premiere of a film adaptation of the classic Oscar Wilde comedy of manners, "The Importance of being Earnest," reports PEOPLE. Fortunately, the inclement weather didn't dampen spirits or prevent the some of film's stars -- among them, Reese Witherspoon (with hubby Ryan Phillippe), Colin Firth and Francis O'Connor -- from attending. Rupert Everett and Judi Dench also star. Witherspoon, 26, who plays love interest Cecily Cardew in the picture, told PEOPLE that it was daunting to be the only American in the cast. "Everyone was so good and so prepared that I felt it was my duty to live up to their experience," she said, explaining that she spent four hours a day trying to sound like a proper Englishwoman and even insisted on speaking with the accent once the camera stopped rolling. But the "Legally Blonde" star still isn't sure whether her intonation would pass muster at a British pub. "It was turn of the century, so it was a little more proper. But I gave it a good, good college try." Costar Firth -- himself British to the core -- concurred, on all aspects of Reese. "I think she's formidable," said Firth, 42, best known as the man who made Renee Zellweger's leading character happy in "Bridget Jones's Diary." "She's incredibly bright," Firth said of Witherspoon. "For someone her age to be so advanced in life -- she's a lot further on than I'll ever be!"