"As with Brad Pitt's and other celeb visits, it'll focus on where America is helping make a difference to save and change lives," said a One Campaign spokesman.

"Lindsay truly does feel for those who are suffering from AIDS and who are poor — she genuinely feels she needs to pay something back to the world for the fortunate life she's led," said the insider. "At the same time, she wants to be taken seriously as a person, and she's well aware of her image as a fluffy party girl. She sees working in Africa as a means to shed her 'naughty girl' reputation.

"Lindsay knows the esteem in which Angelina Jolie is held has increased immeasurably since she started her work with the poor for the UN — and she'd like to be seen as more than an airhead who doesn't care about anything but partying." Lindsay has been beset by rumors about drug use in recent months after she allegedly told a magazine that she tried marijuana. "I'm not going to deny I've tried pot," she was reported as saying, although she later said she'd been misquoted.