Downgrading a psp from 5.03 to 1.5 or 1? Does anyone know something or somewhere I can go?...?

I just got my psp back from my brother( we traded for awhile) and its updated to 5.03, I have my old iso psx images and I would like to play them but i get the copyright protection error. anyone who has actually gotten thier psp to go back from 5.03 please help...I really would like to not brick the crap out of my psp. Thanks everyone.