The hulking security guards standing at the side of a Hunter College lecture hall was a big hint that their usual professor might be taking the afternoon off. When the lights came up and Madonna walked in, that confirmed it.

The former Material Girl surprised students at a film course who had just seen an advance screening of her tour documentary, "I'm Going to Tell You a Secret."

Her appearance was filmed for the mtvU network series "Stand In," where celebrities such as Marilyn Manson, Bill Gates, Shimon Peres, Melissa Etheridge and Kanye West have appeared as guest lecturers at colleges.

Many of the students were about the age Madonna was when she moved from Michigan to New York, determined to make it first as a dancer, then as a singer.

"I wanted to be different," she said Tuesday. "I wanted to be somebody."

Asked by a student what drove her to succeed, the 47-year-old pop star said: "It's one of those things you can't really answer. You're either hungry and determined to make it, or you're not. I know a lot of people who, when they got rejected, they accepted what people said about them. I never did that."

Madonna, who was raised a Roman Catholic, said she was led toward Jewish mysticism following a spiritual quest that began when she had children.

"Being a celebrity, you can get very caught up and seduced into believing and thinking that what you do is the most important thing in the world and get very attached to material things," she said. "I'm guilty of that and I'm still guilty of that, but hopefully I'm becoming less attached."

The wife of filmmaker Guy Ritchie offered a piece of personal advice: "The best thing to do is find one person in your life and try to love them unconditionally. If you've accomplished that, you've accomplished a lot."

Editor: Donald