Te explico cómo lo he hecho yo, no, mejor te pego un post que copié en el foro de DMS es de un compañero llamado AIXI:
First of all, I am Spanish so don't complain about my english
Yesterday I install a dms4pro on my ps2 v9 but i found that there is no support to the devolution mode 1 yet and the only thing you can do is boot an elf that yo have previusly stored in BOOT\BOOT.ELF
After trying things, burn some cds and searching on internet I found a way to make a functional MC loader with the program PS2 KeyLauncher
First of all you need ExecFTPs to upload all we need into de memory card, the DMS hdd explorer instaler already has it, if you don't have a hd try to search it in google (I don't think it would be hard to find).
You also need the PS2 KeyLauncher (
http://www.siirlabs.com/ps2dev/kl/release/ps2-keylauncher-0.4-binary.zip)
The PS2 KeyLauncher 0.4 is only in Spanish but I will explain step by step how to work with it.
Extract the KeyLauncher files and rename PS2KL04.ELF to BOOT.ELF (note that it is case sensitive)
Now load the ExecFTPs on your ps2 and connect to it with a ftp client(I recomend FlashFXP, sometimes you have to refresh manually the directory to see the files). Open the directory mc\0, now create a directory called BOOT (case sensitive) and store the BOOT.ELF that you renamed from PS2KL04.ELF. Now you must have (among other things) mc\0\BOOT\BOOT.ELF
Now you have to save the KL.DAT (the config file of the KeyLauncher), we are going to save the original KL.DAT and we will configure it when we load the program. You need to create a dir named BEDATA-SYSTEM into mc\0\ (you probably already have thi dir created because is the same dir when your ps2 saves its config) and copy the KL.DAT there.
At this point you must have these 2 files into your memory card BOOT\BOOT.ELF and BEDATA-SYSTEM\KL.DAT
Now copy to your memcard all the programs you want to add to the menu (you can copy them wherever you want).I recoment to at least copy the hddloader, ExecFTPs and hdldump (to manage your hard drive through your pc by a lan conection). For example we are going to install the hddloader into the memcard. Create a folder named SOFT into mc\0\ and store there the elf of your hd loader (since there a diferent loaders I'm going to call it HDD.ELF)
Now restart your ps2 and enter in devolution mode 1 and you will load the PS2 KeyLauncher. The program asociate an elf stored on the memory card, the hdd or even an usb drive to the buttons you see on the screen.
To add a link follows this steps:
1- Press strart
2- Select the first option Enlazar un ELF a un boton(link an elf to a button)
3- Select where the elf is (Dispositivo hd is your HD drive and Dispositivo USB is an usb drive), To this example we are going to link the square button to the hddloader that we previusly stored into the memcard, so select Memory card and then go to SOFT and selec HDD.ELF
4- Now the screen shold say this:
Para asignar el fichero:
mc0:/SOFT/HDD.ELF
Pulsa el boton al que lo quieras asignar.
O sea básicamente es así: creas una carpeta que llamas BEDATA-SYSTEM y dentro le pones el archivo KL.dat vírgen que viene con el Keylauncher. Creas otra carpeta que llamas BOOT y dentros le pones el Keylauncher 0.53 renombrado a BOOT.ELF,
Pones las dos carpetas en la memory mc/0 vía FTP y ya está. enciendes la consola y entras en modo devolution 1, en mi caso apretando el triángulo y te sale el keylauncher y entonces le adjudicas los elfs a cada botón que quieras apretando start.
Yo tuve un problema con el BEDATA-SYSTEM, ya que en la memory ya hay un archivo con ese nombre y no me dejaba borrarlo ni grabar nada dentro. Lo borraba desde el navegador de la play ya que es el archivo que se llama YOUR SISTEM CONFIGURATION pero al resetear la consola lo volvía a crear. Solución? lo borro y saco la mamory de la play y se la pongo de nuevo cuando ya estoy conectado por FTP. Espero que te ayude