WARNING My preferred method requires that you perform these steps immediately after installing the game, but before launching it even once. The standard Unreal Engine game method works, but this game has a nasty habit of resetting your FOV to 63 seemingly randomly. My method prevents this. If you have already installed and played the game, uninstall it, making sure you choose to delete your saved games and profiles. You may want to manually back up your saved games first. But if you do, do NOT back up any of the *.ini files that are in the same directory as your saved game.
Now for the method:
Install the game, and do NOT click "play." Go tosystem, and edit DefUser.ini, preferably using textpad. Find these lines:
DesiredFOV=63.000000
DefaultFOV=63.000000
Change the "63" in each line to your desired FOV. I recommend 75 for 16:10 displays and 80 for 16:9 displays. Save it. Now launch the game, create a profile, and set your resolution to a widescreen one from the menu.
That is more work than is necessary. The game keeps profile specific user.ini files that are written over the user.ini file in the game directory when a profile is loaded. The user.ini file in the game directory doesn't actually get "reset", it's just copying in the values from the profile specific user.ini which the above method does not change (direclty). The above method works because you're setting the default before you create any profiles, so all new profiles you create will have that FOV. This is a roundabouts way of doing things though, you can just edit the profile specific user.ini directly.
The profile specific user.inis are kept in the following directory:
C:Documents and Settings[WindowsUserName]Application DataGearbox SoftwareBrothers In Arms[ProfileName]
Where [WindowsUserName] and [ProfileName] name are replaced as appropriate. You just need to change the same two FOV values there.
Also, under Known Issues, it should be mentioned that although the FOV change does affect the environment view, it does not affect the player's in-view gun/hand, so it's not perfectly hor+ as detailed in this post: http://www.widescreengamingforum.com/forum/viewtopic.php?p=88814&highlight=#88814