You can get "widescreen" resolutions running by editing the ini... But the gameplay area itself is 4:3 and black bars are on the left/right. I know I can use a tool to change it, but that only works with 1.3. I got the Platinum Edition of the game, and it comes with 1.51 installed.
Is it possible to get true widescreen resolutions on this thing?
No, the best you can do is use Camera mods to zoom out further. These are perfectly legal for multiplayer, BTW.
http://forums.relicnews.com/showthread.php?t=137248
P.S. If you can't get v1.4 to work then just use v1.3.