This will allow you to downgrade your PSP's firmware from version 2.00 to version 1.50. Check our forums for a tutorial on how to downgrade: http://forums.qj.net/showthread.php?t=18207

MPH's notes:

Requires :
----------
- PSP 2.00 (if you have an 1.51 or 1.52, update to 2.00)
- The 1.50 EBOOT.PBP update ([URL]http://shockzone.free.fr/PSP/Tool/EBOOT_1.50.zip[/URL])
- MPHDowngrader ([URL]http://www.chez.com/mph/[/URL])

Installation :
--------------

- Create a UPDATE folder in PSP/GAME/ folder of your memory stick
- Copy EBOOT.PBP (update 1.50) in UPDATE folder
- Unpack MPHDowngrader.zip
- Copy overflow.tif in your PSP/PHOTO/ folder of your memory stick
- Copy h.bin in root of your memory stick
- Copy index.dat in root of your memory stick
- Plug the AC adaptor
Then, enter in VSHELL PHOTO MENU, this will launch Version Changer.
Create an USB connection and if the Version Changer has been installed, a new file is created in your root of your memory stick (ms0:/index.dat.bak).
Then go to VSHELL GAME MENU and launch 1.50 update.

Follow the instructions ...
MPH