The 200 girls erupted into cheers and applause as the 18-wheeler pulled up to Cabrini High School in New Orleans. Inside was precious cargo—thousands of prom dresses, each tagged with a special note from 17-year-old Marisa West: "I hope you have a magnificent prom!"

Thanks to West, that just might happen. A high school senior from Beltsville, Md., West was buying her own prom dress when she realized that families hit by Hurricane Katrina might not be able to afford gowns for their daughters. "Prom is such a rite of passage," West recalls thinking. "Maybe some girls could go if I send dresses."

A former Miss Teen Annapolis, West grabbed seven dresses from her closet. She e-mailed friends on the pageant circuit and set up a Web site seeking donations—and within months had collected 2,700 gowns for a half-dozen schools. For the young women at Cabrini, where a third of the school's 430 families lost everything, the frilly frocks arrived just in time. "I couldn't ask my parents to buy me a dress," says senior Kaylie Krieger, 18, who tried on a hot-pink gown with a puffy tulle skirt. "The dresses are a dream come true."