You can get some complimentary XMB themes for your PS3 by following the instructions below:
Alternate Lightning XMB Theme
Get the "Master of Time" Platinum Trophy.
Lightnng XMB Theme:
Have a FFXIII Game Save.
Mog XMB Theme:
Get the "Fair Fighter" Trophy.
Noel Kreiss XMB Theme:
Achieve a 5 star rating on the final boss.
Serah Farron XMB Theme:
Get the "Defragmented" Trophy.
Once unlocked, the themes can be downloaded via the title screen.
Edited: Jan 20 2012
Added by: MongooseGeneral Jan 13th 2012, ID#4489