When Tiffany first showed up at the dance studio of Groove With Me on Manhattan's Lower East Side, she was surly, defensive and belligerent. When the other girls began their warmups, says artistic director Courtney Morris '95, Tiffany sat brooding near the wall, unwilling to participate.     That was 18 months ago. Today, Tiffany is one of Groove With Me's success stories--a gregarious, confident, ambitious teenager who is talking about attending NYU. Tiffany is why Groove With Me exists, says Morris.     Founded in 1996 with little more than an idea--that dance might be a vehicle for empowering girls from impoverished homes--Groove With Me has survived on a shoestring. Recruiting from neighborhood schools and community centers, the organization offers free dance training and performance opportunities to pre-adolescent and adolescent girls. By focusing the girls in a disciplined, collaborative program that also is fun and enriching, Morris says, Groove With Me hopes to develop in them stronger self-esteem and a sense of accomplishment.     The program's strength is derived from a solid network of connections, says Morris, who operates Groove With Me along with founder Abigail Rosin. "To give you an idea of the relationship we have with the schools, one of the girls [recently] was having attendance problems and her school actually called us to see if we knew what the problem might be," she said.     The scale is small, she says, but the impact is profound. "We have about twenty committed kids on the Lower East Side and maybe fifteen in our program in Chinatown. Those numbers aren't big, but our relationships are very strong. We are making a difference in the lives of those people."     Morris's interest in dance flourished at Colby. Her senior thesis dealt with the L'acadeo dance style of Jamaica, where she studied her junior year. After graduating and returning to her hometown of Charleston, S.C., Morris worked as a cook until, she said, "I woke up one morning and couldn't stand it anymore." She moved to New York, enrolled in NYU's graduate program in anthropology and met Rosin through her roommates.     Morris would like to expand on her 15- to 20-hour weekly com-mitment to Groove With Me. "If I could do what I do at Groove With Me full time, that would be my choice because it nurtures my intellectual side and my creative side," she said.     When the girls performed at a popular East Village cafe in May, "a legitimate venue" that more seasoned artists would enjoy playing, she says, the pride was evident. "That's my payback," Morris said. "Those small victories; those moments when you see something clicking for the kids, that's what makes this work so rewarding."     Groove With Me hopes to attract funding to secure a permanent studio and to establish itself as a long-term presence in the city. If that happens, she says, the organization may produce more successes like Tiffany.