I think if you're using a wide screen TV the game uses the wide type splitscreen, try setting your XBox to SD mode (push the switch at the back of the connector) then see what happens.

Oh the black areas thingy,
You'll get used to it 

Anyway, yup, I did spot some RE5 split-screen gameplay with no black areas,
If im not mistaken, they said something about messing up with resolution settings.
But that may result in side-effect for dashboard view.

swt...y not they just follow like wat GOW2 did?

i like the gow split screen

if like cod:waw,re-5 the screen will look small

playing in 50inci tv also still not satiesfied

so no solution to it?

Takeuchi explained the reason for that. “It was technically more difficult to make it like it is now than to split the screen in half," he said through a translator. Other options were inferior. Eliminating the black space would have made the players’ view of the action to wide. And it introduced another problem. Without pushing one view to the left and one to the right, the lead characters stood in one column: “Having them on top of each other made it a little difficult to play," Takeuchi said. “We felt that having the characters on different sides of the screen was the best way to play."

if im not mistaken cod:waw also has black screen at the left/right side when playing co-op