possible hoax: proof Chinese discovered America?

An ancient map proves the Chinese discovered the Americas and explored much of the world decades before Columbus, a Chinese antiquities dealer says. A brief report from National Geographic News says the dealer was alerted to significance of the map after reading 1421: the year the Chinese discovered America, an investigation by an amateur historian.

The map is now being dated, but my guess is it will turn out to be a hoax, or at least won't survive as proof of Chinese exploration—although I would love to see solid proof that the Chinese did come here then.