sry i only have a german tutorial:
Tutorial zur Erstellung eigener Menu Hintergründe in Battlefield 2 - Inhalte - Crysis News
but i think its not that hard^^ you only have to open the picture you want to have as background and click "bink it!"... in the upcoming window you can change settings etc etc..but i always use the default ones

...there you can also change the path where the converted picture should get outputted (if you want to change the menu background you have to save it as
menu_loggedin.bik in your
EA GAMES/Battlefield 2/mods/bf2/movies directory..overwrite the old one (
make a backup before)and you're good to go

greetz
ps:sry my english
