The games will most likely be able to link to Diamond, Pearl and Platinum as shown by game data.
HeartGold and SoulSilver will be released in Japan this fall, possibly on or near Nov. 21, the 10th anniversary of the original release of their namesakes. International releases will likely come in mid-2010.
UPDATE!!!
WHAT THE **** IS THIS ****? WHERE'S KRIS? COMMENT ON THE THREAD!
UPDATE 2!!
The DS will use its 3-D feautres when selecting a start pokemon, new sprites for the starters are out!
MAJOR UPDATE!!
HeartGold and SoulSilver will come with a pedometer, which allows you to put in a Pokemon and level it up as you walk.
Update:A new image has surfaced from people from 2ch who have copies of CoroCoro. It states that the Tanabata event Jirachi, previously available by entering the Pokémon Daisuki Club's raffle, will be available at selected McDonald's restaurants from June 19 to July 17 to all players of the Japanese version of Diamond, Pearl, and Platinum. Screenshots from the upcoming WiiWare game Melee! Pokemon Scramble! also appear at the bottom of the page. The game will be available for DS Download Play around the same time as the Jirachi event. Rumors say that a Jirachi can be obtained from the said game and trading it to HeartGold and SoulSilver will unlock a new area called Edge of the Night Sky.
Another two scans from CoroCoro also surfaced, revealing the boxes for HeartGold and SoulSilver. They are a bit bigger due to the PokéWalker being included. The cover shows different artworks of Ho-Oh and Lugia from the ones found on the official Japanese site. Behind them is the map of Johto, with the Tin Tower and Whirl Islands being included on the cover of HeartGold and SoulSilver, respectively.