To access the hidden Challenge Room, just enter the following code at the title screen, where the BCR logo is shown, before the intro starts again. You can use the D-pad or the analogue stick for the directions, and they'll work on the PC version too, provided you have a controller.
Aaron Sedillo's Room
Xbox 360: Right, Down, Left, Up, Left Bumper, Right Bumper, Y, Y, X, X, Start
PS3: Right, Down, Left, Up, L1, R1, Triangle, Triangle, Square, Square, Start
We've also hooked up (hah!) with several different websites and games publications to offer their own exclusive rooms too - and whereas I could beat Aaron's room without too much fuss, these have the difficulty level pumped all the way up to "Devil May Cry 3". Downloadable content? Bah! This is how we used to give away extra content back in the day! Be warned: you'll have to re-input the code when you restart your system, and these work in English language only.
Eurogamer Challenge Room
Xbox 360: Down, Up, Down, Up, Left, Left Bumper, X, Left Bumper, X, Y, Start
PS3: Down, Up, Down, Up, Left, L1, Square, L1, Square, Triangle, Start
GamesRadar Challenge Room
Xbox 360: Right Bumper, Y, X, X, Up, Down, Left Bumper, Left Bumper, Up, Down, Start
PS3: R1, Triangle, Square, Square, Up, Down, L1, L1, Up, Down, Start
IGN Challenge Room
Xbox 360: Up, Down, Y, X, X, Y, Down, Up, Left Bumper, Left Bumper, Start
PS3: Up, Down, Triangle, Square, Square, Triangle, Down, Up, L1, L1, Start