Original: Pokémon Platinum, the enhanced version of Diamond and Pearl, much like Pokémon Yellow, Crystal, and Emerald, was released September 2008 in Japan, March 2009 in North America, and is scheduled to be released in Australia and Europe in May 2009.
Simplified: They were released in Japan in 1996, then in North America in 1998 and finally in Europe in 1999. In 2007, Pokémon Diamond and Pearl were released. A sequel to Diamond and Pearl, Pokémon Platinum, has been released in Japan, then it was released in the United States in March 2009.