Xtrusion has released a new, PC-based downgrader for firmware 2.50/2.60 PSPs, built off of Dark_AleX, Matheliuh, and Yoshihiro's work. It's an easy and safe installer which helps install the neccessary files and requirements, making downgrading a breeze for those with a little less than par PSP knowledge. You'll still have to acquire the neccessary 1.50 firmware dump files on your own though, due to legality reasons. Great work Xtrusion, many newcomers to the scene thank you for your hard work!
Download Easy 2.50/2.60 Firmware Downgrader Light from PSP 3D
here.