I just downgraded my psp from 3.03 to 1.5 to see what potential it has,so i put ir remote in it (fun and works on all my ir stuff) then i put psp dev hook v0.22 in it, and then a umd emulator (not to sure what these to things do exactly but im sure i need them at some stage, or now!!!)
i downloaded a small game to test if it will work,the game is called PHROV its from.
i created i ISO file in the front of the psp usb area were there is psp, photo, mp_root, etc. when i open the game file that is on my pc,the folders are, PSP, and inside that the folder is GAME150, and inside GAME150 there is to more folders called PHORV% and PHORV,the problem im having is i dont know what goes where,and have i downloaded the right programs that are up the top of the page.
I am currently in the same situation as you. I downgrade recently from 3.03 to 1.5 successfully. I however plan to upgrade to custom firmware (3.03 OE-C), there appears to be plenty more support for this and also has a recovery mode incase it all goes wrong. It is of course your own decision.
You will find more help if you were top post in forums such as:
