Before you attempt this firmware install, if you have already installed custom firmware on your PSP this measure might brick it. Don't double install if you have already hacked your PSP.
All files you need to install 4.01 M3 to PSP are available at the following address / URL. This custom firmware will allow you to expand the things you can do with your PSP.
Dark_AleX and Team M33's custom firmware 4.01 M33.
Bug fix: vshmenu didn't let change camera mode due to camera_plugin using select button. Fixed, now vsh menu will not be loaded when using the camera.
Recovery can now be translated, See how below. Translation to Spanish is auto included.
Updated the M33 SDK with a new function and sample, and released the psp-packer tool to compress prx's and PBP's in the ~PSP format.
The folder of 4.01 and higher homebrew will be GAME4XX so it won't need change on update.
ALL THE FILES NEEDED TO COMPLETE THIS INSTALLATION CAN BE DOWNLOADED FROM THIS ADDRESS