Things You'll Need
Instructions
Attach your customized PSP to your computer using a USB cord and turn your PSP on. On your PSP go to "Settings>USB connection." A PSP folder should appear on the desktop or in "My computer" representing the PSP memory card. On a PC, this is usually the "E" drive. Sometimes the folder is unnamed, but opening it will reveal the PSP folders.
Eject the PSP from USB mode by dragging its icon to the trash (on a MAC) or by clicking the option "Eject" (on a PC) and then quitting USB mode on the PSP. Keep the USB cord attached, because your PSP sends more data to the computer in step four.
Shut off the PSP by holding the power switch for five seconds. Turn it back on while holding down the R trigger. This starts up the PSP in recovery mode.
Select the option "Advanced" and then "Toggle USB flash 0." A folder pops up on the computer, the same as in step one, but the contents are different.
Go to the "Vsh>resource folder." There will be a lot of files here. One of them is called "gameboot.pmf." This is the file that tells the PSP what animation to play when loading a game. Make a copy of this file and keep it as a back up somewhere on your computer, then delete the original. If you do not make a back up and something goes wrong, you will have no way to restore your PSP's original settings.
Find the custom gameboot file that you want to load on the PSP and rename it if necessary. The file should be called "gameboot.pmf." Put it in the resource folder.
Exit recovery mode. The next time a game is started, it will play the customized gameboot screen instead of the usual PSP loading screen.