Beckham: Danced "to make people watch me"
The singer, 26, who recently announced she was expecting a second child with footballer husband David Beckham, also said she wished her musical model had been "someone a bit cooler".
Her admission came on a new documentary for ITV1 in which she talks about her childhood involvement in music and dance.
"I've always loved singing, I've always loved dancing and this is the one thing that I could do to make people watch me and pay attention to me."
The singer recalled watching Manilow with her mother at a rainy open-air show at Blenheim Palace.
"She said 'I'm going to be up there one day doing that'," her mother remembered.
Beckham said watching the TV series Fame was another spur to her career: "It wasn't until I saw Fame that I thought 'That is it, that is what I want to do'.
She also revealed she did not like chart rival Kylie Minogue's single Can't Get You Out Of My Head - which beat her to the number one spot in November.
Faint praise
"When I first heard that record, if I'm being totally honest, I didn't like it," she said.
"I like a song that has lyrics, a good melody. I can't dispute that it has a catchy feel but I like a song that has a bit of emotion."
Beckham also said her occasional weight problems dated back to joining a dance school in her teenage years.
"They do weigh you, they do make you very conscious about your weight," she said.
"On the one side you think that's terrible, it can make you have eating disorders, but the other side says, yes but to be a dancer you do have to be small."
The documentary also records some rather faint praise from one of Posh's former teachers, Joy Spriggs.
"If Victoria hadn't had the lucky breaks that she had and the people having faith in her to make her what she is, she probably would have been singing and dancing on a cruise liner," said Ms Spriggs.
"There are lots of girls with more talent, I'm being quite honest here, that are doing less than Victoria's doing."
Being Victoria Beckham, ITV1 at 2100 GMT, Monday 3 March