I reversed the game and figured out the encryption used on the BF3 resources with the 0x00D1CE00 header magic. Just run it once on the file to decrypt it, and once again to re-encrypt it. The crypto is just a simple XOR encryption with a per-file key and a constant. I did this for the PC version, if this does not work for the xbox 360 just send me the a few files and an xex and I can fix that.
Source is included. Compile for linux with "gcc -Os bf3decrypt.c -o bf3decrypt"