In the bit where you try and sneak into the Suzzaro Mansion, there is only one way of getting in. This is it.
Near the Jeep, put the handbrake off and then use the car Jack handle to prise off the Car Jack. Push it forward then climb on top of it to get onto the wall. When you are there, try and climb the drainage pipe george is the only one that makes it.
You are now Nico. pick up the metal bracket off the ground and climb down off the Jeep, and to the Limo. Get on top of it and open the window by using the bracket.
To unlock the extras option you need to complete the game once and then save the game. When you go the main menu there will be an Extras option in the main options menu.
Included in Extras are Concept Art and Character Sketches.