What has Kirsten Dunst been doing since she said goodbye to Spidey three years ago? Changing her life.“Most people my age probably stop for a second and question, ‘Is this really what I want to do?' ” says Dunst, 28, who started acting in commercials when she was 3. “I took some art classes. I moved to New York and did my apartment. I made a short film. I'm definitely different now.”Perhaps most