EDIT: The bundle is actually available at a variety of stores, not just Gamestop. Amazon.com has it with free shipping, and Circuit City is giving the bundle away with a free action figure. All major retailers are probably getting them, like Target, Toys R Us, Wal Mart, etc.
According to Pokemon.com, the Dialga and Palkia Nintendo DS Bundle will be available at stores starting this Sunday, August 17th. The price of the entire bundle is $129.99. Since the bundles are limited edition, they’ll probably go fast, so jump to it if you are going to buy one!