All you need to do is copy the 2 folders in MS_ROOT into your PSP memory stick root, and lauch DevHook.

Set DevHook to firmware 2.50 + 2.00 and other settings as follows:

UMD Select: Select Your iSO File
UMD Mount: ISO ANYUMD
Firmware: 2.50+2.00
Boot Select: Reboot XMB
UMD Version: 2.XX -> 2.00 (set it, or you will get a 2.6 error)
CPU Clock: 333 MHz / 166 MHz

NOTE: This Firmware is in English - replace the flash1 in dh/200 and dh/250 with your own flash1 in your language.

This version redirects flash access to Memory Stick.