So why in the world is Cameron Diaz, one of Charlie's Angels, the voice of Princess Fiona (Mrs. Shrek) and girlfriend of Justin Timberlake, trekking from Yellowstone National Park to Chile to Africa and other environmentally imperiled locales with a camera crew in tow? "To show everyone how beautiful this planet is and how we're all connected to it," says the eco-activist actress at the outset of this breezily paced 10-part series. Despite Diaz's admirable goal, Ego-Trippin' might be a better title for her show. On each leg of her journey, she recruits celeb pals such as Jessica Alba, Drew Barrymore and Kid Rock to accompany her. For the March 28 opener, a visit to Nepal, Eva Mendes (Hitch), hip-hop artist Redman and Blink 182's Mark Hoppus and his wife tag along. Interspersed with their close-up views of endangered Asian one-horned rhinos, crocodiles and elephants, we see Diaz blithely dismissing the camera crew so she can shower after a sweaty day of sightseeing (well, she is the executive producer) and learn that tentmate Mendes is arachnophobic. "How is the spider situation?" she asks their Sherpa guide. Fans who want to know more about Diaz's personal situation should catch the May 23-30 two-parter in Tanzania, where she's joined by beau Timberlake.