Yoshihiro, once again, just send us a utility that will please a number of you. A utility to run games on 5.55 Custom Firmware "GEN"
Yoshihiro, we no longer need to present, has created a utility to decrypt the 5.55 eboot games and who do not yet passed on any custom firmware posted. Clearly, you'll be able to run games requiring firmware than the one installed on your console and games like MotorStorm should pass on all the consoles and custom firmware 5.50GEN even 5.03GEN. It is not beautiful life with the team "GENyUS?

MotorStorm turn on 5.03GEN (PSP-3000 and PSP-2000 v3)
and 5.50GEN (PSP-2000 and PSP-1000)
To make it work, it must have the original and know how to use the utility UMDGen v4 (a tutorial will be available at the output) into an ISO. Otherwise, we will explain everything to the output of this utility tonight.
WARNING
use an ISO without having the original is prohibited by law and punishable by imprisonment and heavy fines. Buy your games will allow the PSP to survive with good titles.
MaGiXieN Note: This should end all the rumors that the poor launch sites bad reading or bad notoriety, our inability to decipher anything or to treat our members like dogs. We will give you more information on any Advanced Custom Firmwares GEN in a news ahead and we'll also enjoy a 6.00 SAUSAGES (attention inside humor) you tell us the news.
Source: hxxp://pspgen.com
DownloadGame Decrypter v1 by Team Gen: http://www.mediafire.com/?jzjjttdozyvInstruction:
Here's what's everyone is waiting for
Game Decrypter by Yoshihiro
..:::Yoshihiro's 5.55 & 6.00 games decrypter:::..
hi guyz this tool is here for let you use your original game backup
on Custom Firmware 5.50 gen B-2 .
how i can use this tool ?
1 :lets go first you need to install the GameZDecryptZ folder in your X:PSP/GAME folder
2 : put your EBOOT.BIN extracted from UMDGEN PSP_GAME/SYSDIR and put it on root of your memory stick
3 : now you can boot game decrypter now you can press X 5 seconds later it's done 
4 : connect your usb cable check on root of your memory stick you have a new folder called decryptor
5 : copy the eboot.bin from the decryptor folder inside umdgen and rebuild your iso
VoilÃ
Enjoy it Yoshihiro 
PS : not all games working because some games use some fact header on prx files DOWNLOAD HEREGame Decrypter Version 2MEDIAFIRE DLTHis also contains version 1 and UMD Gen v.4 downloads
MegaUpload DLRapidShare DLlinks courtesy of Yuan of psiso
This v2 will now enable you to decrypt and patch Marvel Ultimate Alliance. Personally tested by me to work.