Mostly they deploy a 4-4-2, with two central mids and two wingers. Depending on the game, it could turn into a 4-3-3 sometimes. With the left winger(Robinho, Bellamy or Petrov) moving upfront, and SWP(who is their right winger) slotting in central mid. But it is primarily a classic 4-4-2 that they deploy.
Today both Robinho and Tevez are probably going to miss the game. So i'm guessing this is how their lineup will look like:
-------------------------Given-------------
----Richards-------Toure------Lescott----Bridge
------------------Ireland------Barry
---------SWP--------------------------Petrov
---------------Bellamy------Adebayor
The thing with this formation is, that Ireland is being forced to play deeper than he likes to, which has affected him negatively this season. I watched their games against Wolves and Blackburn and i noticed that Ireland isn't half as dangerous as he used to be now that he is playing deep. He's an attacking midfielder imo not a central mid.