Change the resolution to one that is widescreen. If there aren't any widescreen resolutions in the options then you can use the desired reso by putting +szx XXXX +szy YYYY after the path line of the BF2 shortcut.
So for example if you want to make your reso 1024x768 then the path should look something like:
"C:\blaablaablaa\Battlefield 2\BF2.exe" +szx 1024 +szy 768
Not sure if you need to put +widescreen 1 somewhere in there, but if you do then it should look like
"C:\blaablaablaa\Battlefield 2\BF2.exe" +widescreen 1 +szx 1024 +szy 768
(note that 1024x768 isn't a widescreen reso)
also, bf2 isn't that great when it comes to widescreen.
I recommend you check out this program: http://imk.cx/pc/widescreenfixer/