Here are interviews with J.K. Rowling, Daniel Radcliffe, Rupert Grint and Emma Watson. I'm sorry I haven't added any more artists who played in Harry Potter but I will as soon as I get the chance.

J.K. Rowling
Scholastic Online Chat Transcript - February 2000
Houston Chronicle Interview - March 2001
Raincoast Books Interview [Comic Relief Books] - March 2001

Daniel Radcliffe
Nickelodeon Magazine Interview - Oct. 2001
BBC Films Interview - Nov. 2001
StudioLa Interviews Daniel Radcliffe - Nov. 2001
Rupert Grint
Nickelodeon Magazine Interview - Oct. 2001
Emma Watson
Nickelodeon Magazine Interview - Oct. 2001