Toni Collette is one movie actress who is flattered when you don't recognize her.

''I don't get frustrated if people don't know who I am,'' says Collette, who plays a deeply depressed hippie mother in About a Boy. ''I actually get a kick out of it because it means I'm doing my job properly. I'm becoming somebody else; I'm creating somebody else's reality. It's not about me.'' So it doesn't really matter if you recognize Collette as Haley Joel Osment's frazzled mom in The Sixth Sense, as the chubby ABBA fanatic in Muriel's Wedding (she gained 40 pounds for that one) or the skinny rock wife in Velvet Goldmine (she lost more than 40 for that one). She's also in Changing Lanes, Shaft and Emma, and still, few people recognize her on the street. ''I'm glad that I can still walk down the street because I can't imagine having that taken away from me,'' says Collette, 29. ''I really feel for actors who are so famous that they literally cannot walk down the street. That would be a sad way to live. Your career would be everything to you. I love acting, you know, but life is bigger.'' Collette, who is single, has been so busy for the past several years that she ''lived out of a suitcase,'' but she recently bought a house on the beach in Sydney.

Collette learned just how convincing she is when, as a child in Australia, she so authentically faked the symptoms of appendicitis that a doctor removed her perfectly healthy appendix. She might still be having body parts removed today had she not become a professional actress in Australia and now the USA. ''The world is shrinking rapidly, which is good for actors because I get to play Americans, and Americans get to play English people, and English people get to play Polish people and Polish people get to play Australian people,'' says Collette, who was nominated for an Oscar for The Sixth Sense and for a Tony for the stage production The Wild Party. ''There are cultural differences, but I think that essentially we're the same on the inside.'' But sinking so completely inside a role is something that actors of most nationalities cannot do. Collette says it's a mystery to her. All she knows is that she will play a role only if it ''resonates'' with her, then she ''digests'' the part. ''So even I can't tell if it comes off the page or whether it comes from in me.'' According to Paul Weitz, who wrote and directed the film with his brother Chris, Collette becomes so connected to the script that it's impossible to change a line or encourage her to improvise.

''I think she believes that the character is really saying the lines,'' he says. Collette likes Boy because it's ''very lifelike. It's innately very funny -- like (wet)-your-pants kind of funny. And it's also very moving and poignant and deals with a lot of subject matters quite gracefully.'' For Paul Weitz, Collette's ability ''to do comedy and drama at the same time'' made her perfect for the role. ''She's a top draft pick,'' Chris Weitz adds. ''It's like getting Michael Jordan to be in your movie.''