Here is a press release that gives a description of the first three stories. Even though the release says returning this fall it was leaked at the BFI that September 1st is the air date and still awaiting official word from the BBC on that.
Doctor Who returns this autumn to the BBC, starring Matt Smith, Karen Gillan and Arthur Darvill as they head off on five epic adventures.From Daleks to Dinousaurs and an alien with a grudge, this series features a whole host of guest stars, including: David Bradley, Rupert Graves, Stephen Berkoff, Mike McShane, Ben Browder, Adrian Scarbourgh and Anamaria Marinca.
Episode 1: Asylum Of The Daleks - Kidnapped by his oldest foe, the Doctor is forced on an impossible mission - to a place even the Daleks are too terrified to enter... the Asylum. A planetary prison confining the most terrifying and insane of their kind, the Doctor and the Ponds must find an escape route. But with Amy and Rory’s relationship in meltdown, and an army of mad Daleks closing in, it is up to the Doctor to save their lives, as well as the Pond’s marriage.
Episode 2: Dinosaurs On A Spaceship - An unmanned spaceship hurtles towards certain destruction - unless the Doctor can save it, and its impossible cargo... of dinosaurs! By his side a ragtag gang of adventurers; a big game hunter, an Egyptian Queen and a surprised member of the Pond family. But little does the Doctor know there is someone else onboard who will stop at nothing to keep hold of his precious, prehistoric cargo.
Episode 3: A Town Called Mercy - The Doctor gets a Stetson (and a gun!), and finds himself the reluctant Sheriff of a Western town under siege by a relentless cyborg, who goes by the name of the Gunslinger. But who is he and what does he want? The answer seems to lie with the mysterious, Kahler-Jex, an alien doctor (yes another one!) whose initial appearance is hiding a dark secret.