[{HVY-E}Jinxx]

First, you need to make sure that your Video Card/Monitor combination will support it.
Since I don't know what you have, I'm going to assume that you have already checked on that.

Open the conf.ini in the root directory of IL-2.
Change the resolution at the top of the file to what you want.
Make sure that you set save aspect to 0.

Now, last, but not least, if you have Vista or Win 7, you will have to make sure that you have set UAC to Off or make sure the game is not in the Program Files directory.
The reason for this is any system file, (ini's are considered system files by Vista/Win 7), has a backup copy made at the start of the program. That file is then compared to the original upon program termination. If any changes have occurred, Windows will then copy the backup over your changed file bringing the file back to it's original state.

That means any changes you make to your conf.ini file will be changed back to it's original (install/setup) state when the program ends.

Hope this helps you out.

S!