The images are normal gif pictures. It is advised to resize them to fit your screen size.
The startup sound is an mp3.
Here comes the file names:
Startup image: STARTUP_IMAGE_SEMC
Shutdown image: SHUTDOWN_IMAGE_SEMC
Splash image(the SE logo what you see when you turn on the phone): SPLASH
Startup sound: STARTUP_SOUND_SEMC.mp3

Copy the files to phone's /tpa/preset/system/settings/ folder.