Get the PSARDUMPER for 5.00 HERE

Move it to /PSP/GAME5xx

Download the 5.00 EBOOT HERE

Move that to the root of your MS.

When done:

1)Disconnect USB, and launch the PSARDUMPER as you would a homebrew, etc.
2)Press [] once its loads.
3)Wait. When it is done, the PSP will exit to the XMB.
4)Re-enable USB Connection.
5)Decrypted files can be found at ms0:/F0 (The F0 folder on the root of your MS)
6)PRXs are going to be in F0/kd, and F0/vsh/module

Have fun.