You need another PSP with a custom firmware, and here's soemthing I posted before on another topic, this will make it easier for you to get it:
DO THIS AT YOUR OWN RISK!!!
Go to the two following links and place the two things that you will download (EBOOT.PBP and kstuff.prx) into a folder called pan3xx:
1.)
http://www.sendspace.com/file/ehctoz
2.)
http://www.sendspace.com/file/91e0y0
Then, go to your PSP's memory stick and backup all of the saved files onto your computer because you will have to delete all of the data on your memory stick. Then, delete all the stuff on your memory stick. Next, create a "PSP" folder and a "GAME" folder inside of it. Then, place the pan3xx folder inside that game folder. Next, download this file and place it on the root of your memory stick:
http://www.sendspace.com/file/d2dqe8
After that is done, put your memory stick into your friend's PSP, and turn of the PSP plugged into the charger with the made in china battery inserted. After that, turn on the PSP and go to the game saction and go to the last option of "memory stick" then run the application on your PSP. When the menu comes up, press, R+X to properly format and ext the application an dturn off the PSP. Then, make the PSP and GAME folder again, and put back the pan3xx folder in the GAME folder. replace the EBOOT.PBP on the root of your memory stick. Go back to the psp and turn it on and run the program again. Then, press X "to install 1.50" then press L+X "to install msipl.bin". After that, press O to make your battery a pandora one. Then, exit the program and turn off the PSP. After this:
FOLLOW DIRECTIONS EXACTLY!!!:
1.) Take the memory stick out of your friend's psp
2.) Take the battery out as well
3.) put the memory stick into
YOUR OWN PSP
4.) the psp should automatically turn on.
5.) Press the button to downgrade the PSP
6.) folllow directions
7.) go back to the PSP and run the application again and press O to revert your battery back to normal.
8.) you now have version 1.50, from there, upgrade to any custom firmware you want.