This is the New Custom Firmware (CFW) 6.60ME 1.2 This fixes a few bugs and also enables a new CPU feature.
Take the files after downloading and extract them and you should see the release folder. On the root of the PSP memory Stick create a folder, if you haven't already, and call it "seplugins" (NO QUOTES) and open that up. Create a "game.txt" or open the one you already have up and inside write "ms0:/seplugins/leda.prx 1" and then exit and save the txt document. Once that has been done open up the leda folder in the extracted files and the drag and drop the leda.prx into the seplugins folder. If you have one there already, replace it just to be safe.
Now take the UPDATE folder from the extracted files and drag and drop the UPDATE folder into the PSP game folder other known as ms0:/PSP/GAME and then exit USB mode and run the installer on the XMB and your done.
If you are running CFW lower than 6.60, all you need to do is take the OFW Sony 660.PBP that i have for download and place it in the UPDATE folder inside the PSP GAME folder along with the CFW installer for ME 1.2
NOTE: This is only for PSP 1000 and 2000 hackable models