From Ask Ausiello
:Question: Do you have any information regarding Prison Break's future? Is there any hope of getting all 22 episodes this season? -- Adry
Ausiello: Well, there is now. Not so much two weeks ago, when Fox told producer Twentieth Television that they only needed 16 episodes this season instead of the originally-agreed-upon 22. (Quick sidebar: Ironic that the network would make such a request this season when the show's actually good. Where were they last season when it sucked!) Anyway, Twentieth's response to Fox went something like this: "You asked for 22, you're getting 22!" So, to answer your question, Adry, yes, there will be 22 Prison Breaks this season.
PHEW! and HURRAH!