in /TPA/PRESET/SYSTEM/SETTINGS
there are:
BOOTUP_IMAGE (animated gift at start up)
BOOTUP_SOUND
SHUTDOWN_IMAGE
SPLASH (static image:sony ericsson logo with black background)
With FAR manager (i can't be able to use it) you can save a copy of the file in computer. After is simple: rename SPLASH to SHUTDOWN_IMAGE and put into the phone the renamed file with xs++.