Andriasang: D3 Publisher had to make four different packagings for the upcoming PSP title Earth Defense Forces 2 Portable. Have a look here.
Andriasang: PSP's upcoming Earth Defense Forces 2 has two forms of multiplayer: co-op and battle. Both offer four player support.
Earth Defense Force Portable 2 lets you engage in aerial combat using either a jetpack or a vehicle.
Andriasang: D3 makes an official announcement about the PSP title and its unbelievable special package.