I finally got it to work. Hope this helps:
At first get the iso and hook boot (you can grab it from psp-spot). Copy the iso content called "PSP_GAME" to the root of your memory stick and the hook boot files to PSP/GAME.
Start hook boot. Select UMD Emulation by pressing circle. After that press X for file. At the next 2 questions press until the message "MARK & HOOD NID" appears on the display. Then it goes on with the kernels:
Press X for "No Hook" at the first two questions and circle for "Hook" at the following questions. Finally 12 files must be hooked. Then follow the instruction on the display. Last word: Sorry for 3 posts but i'm browsing with psp and reached word limit.
EDIT: Posts merged by Chouonsoku. No probs for the PSP users