Choices you've made in Season 1 will carry over to The Walking Dead: 400 Days and the choices in that will show it's impact in season 2.
The new episode is set to launch in next month for $5 and PC, Mac, XBLA, PSN and what caught me by surprisingle, iOS. The PSVita version will come out in August of this year and it will be bundled with the entire first season.
Some of you maybe not be pleased that this isn't season 2 but hey, I'm just glad that we're getting more Telltale Walking Dead action this early. And don't worry, season 2 is due out later this fall.