Ali Mohamed remembers little of the fire that claimed the lives of his father, his uncle and his grandmother in Somalia and took both his legs when he was 8 years old.

That was a dozen years ago, before he'd fled to safety in Kenya and then taken his first airplane ride to America, where an older sister had settled in Woodbridge.

In 1999, Mohamed arrived at sprawling suburban Gar-Field High School, speaking not a word of English and whipping through the halls in the first wheelchair he ever had.

Determined not to be overwhelmed by his past, he adopted as his motto one of the first English sentences he learned: "Don't worry, be happy!"

Members of the new family he made at the school wanted still more for him. They wanted to see him walk.

They got their wish yesterday.

Sporting a wide grin, the 20-year-old senior made his first appearance at Gar-Field on new state-of-the-art prosthetics -- for which his community had raised funds -- that use computer chips to simulate the motion of the human leg. Teachers and students wiped away tears, applauding for Mohamed as he navigated from his school bus to the school door on his new legs and crutches.

"Thank you so much," he kept saying, his smile never dimming, as the clapping continued with his every careful step. "I really appreciate it."

His triumph injected a bit of festivity into the day. "Ali Baba!" shouted some of his classmates when he arrived in his first-period class. Exclamations of "What up, Ali!" and "I like your new shoes, Ali!" followed him through the halls. As school let out, some students rushed to their classroom doors to see Mohamed walk by. "He's a student icon around here," said Assistant Principal Robert Scott.

It's hard not to get wrapped up in Mohamed's upbeat personality, said Jean Ellerbe, who runs a learning lab for students who need extra help with school work.

"He just knows how to fit in so well," she said. "He has never, ever said, 'Oh, I can't do this because I don't have legs.' "

A year ago, the prospect that Mohamed would walk was just a dream. Knowing that the new legs would cost about $45,000 apiece, Ellerbe made it a class project for her students to write to Oprah Winfrey and Maury Povich, hoping their attention might lead to a donation. A newspaper sponsored a basketball exhibition on his behalf last year that raised $8,700. One teacher said she got $100 in change from students. A motorcycle club in Quantico, hearing his story, kicked in $500.

Ultimately, Mohamed's insurance company, UniCare, would handle the costs, said Johnny E. Baskin, the prosthetic specialist who fitted him for his legs. The money raised by the community will cover other things Mohamed needs: namely a car, so he can get a job to earn money for college.

"I have to drive and go to NOVA and work," he said, referring to Northern Virginia Community College, where he hopes to learn how to be a computer technician. "You feel better when you are driving and going to college."

Mohamed said he lost his legs when militia members firebombed his house. His mother fled with his siblings, believing him dead, and learned only months later that he had been rescued and taken to a hospital.

"I'm so happy to see my mother. I don't see any family when I'm in the hospital," he recalled. There wasn't much medicine in the hospital, and not enough time for staff members to comfort one child with a missing family. "Sometimes you cry by yourself," he said.

Fleeing to Kenya, the family lived first in a refugee camp and later in Nairobi until Mohamed's sister Zahra was able to arrange their travel to the United States. By then, Mohamed said, he had learned to move pretty well using only his hands and arms.

But America was bewildering in many ways, he said -- like the weather. He saw snow for the first time. "It was unbelievable!" he said.

At Gar-Field, where he arrived with a sister and brother who also spoke no English, he doubted he'd ever fit in. And additional surgery kept him back a year in school.

"I never thought they would treat me like a regular person," he said. "I thought they would say, 'You don't know how to walk.' But I never see anyone making jokes."

His physical therapist, Lisa Kelly, said Mohamed manages to keep a sunny attitude even when he's on the treadmill, "sweating his fanny off. He is the most positive person I've ever met. He always comes in with a smile. He always tries to make you smile."

Mohamed has been fitted with prosthetic legs before, but the older style was hard to maneuver because much of his thigh tissue is gone. He has had the new devices since February and has been working steadily on them to improve his balance and coordination. The C-Legs prosthetics, manufactured by Otto Bock Healthcare, have sensors that provide continuous adjustment to the legs, making it easier for Mohamed to maintain his balance. In time, Baskin said, he'll be able to walk without crutches. "It just takes confidence," he said.

That's one quality his therapists, teachers and others said Mohamed appears to have in abundance.

"If you feel sad, you never get anything," Mohamed said. "If I am sad and not happy, then I'll be very disappointed and I'll never make my life better."

The wheelchair days are now over, he said. He's already on his way to his next big step -- across a stage two weeks from now, to get his high school diploma.

Ali Mohammed gets an enthusiastic welcome at Gar-Field High School. "He's a student icon around here," Assistant Principal Robert Scott said.Yonis Mohamed, left, helps his brother Ali put on his new prosthetics before school. Ali Mohamed plans to work and attend Northern Virginia Community College.