Way in the back (page 93 to be exact) of the October 2007 issue of Nintendo Power is a tiny little article... but, it contains IMPORTANT INFORMATION for all Pokemon Diamond and Pearl game owners. Below is the article as it appears:

Manaphy is a special Pokemon that you won't be able to find normally in Pokemon Diamond or Pearl; until now, the only way you could snag it was to find a Manaphy Egg in Pokemon Ranger and transfer it over. But now there's another way to get the Legendary Pokemon; on September 29 between noon and 3 pm, head to a participating Toys "R" Us store in the United States to obtain a special Manaphy that you can't find anywhere else. Bring your copy of Pokemon Diamond or Pokemon Pearl into the store to download a Manaphy just like the one in the latest Pokemon movie, Pokemon Ranger and the Temple of the Sea. The Pokemon will be holding a Red Scarf like the one in the animated feature, and it will be enclosed in a Cherish Ball-a Poke Ball that is otherwise not available when playing Pokemon Diamond and Pearl. When you release a Pokemon from the Cherish Ball, a colorful animation appears, Manaphy is also the only Pokemon to have the the move Heart Swap, which allows it to switch all stat modifications with an enemy. Don't miss this opportunity to get such a rare Pokemon! For further details check out pokemon-games.com or toysrus.com.

So, to recap... take your Nintendo DS and Pokemon Diamond or Pearl game cartridge to your local Toys "R" Us tomorrow between between noon and 3pm for this special event to obtain Manaphy.