Black border around Halo 3 multiplayer/co-op?

[Italian Stallion]

In Halo 3, whenever I use Co-Op or multiplayer using split-screen, something happens. The screen "shrinks" and gets pushed together, making about 3 inches of black border around the screen, so I have even less viewing area than usual. Yet, when I went to a friends house, the screen was perfectly normal and widescreen. Also, I have a 26" Panasonic HDTV. With my other games, this never happens. Help!!
As a side note, I noticed in the HD plugs for my friends Xbox 360, the yellow HD plug was connected to the TV, and mine isn't, because there isn't a slot for it. Don't know if that helps.

 

[Kenneth M]

your screen isn't set up right. it IS HDTV comp. on the collectors eddition bonus disk it has a tutorial for calibrating your HDTV's. so, your screen just isn't calibrated right

 

[danguy01]

Happened for my friend. All I know is that Halo3 isn't HD able