Well, The Legend of Zelda: Spirt tracks or The Japanese Title is Zeruda no Densetsu Daichi no Kiteki Translate to The Legend of Zelda: (Train) Whistle of the Earth,
No one Knows the Story line yet but a Theory states that Spirit Tracks takes place 100 years after the events in Phantom Hourglass.
if you wanted to know more about it, check Zeldapedia
link
All I really know is it's coming out late 2009 (I think)
The game is Very un knowing right now, But not as much as the new major Zelda game for the wii