Heres a newspost sourced from and better explained by PSP3d
FreePlay and Skylark have released a new Windows binary tool used to convert standard TrueType (TTF) fonts to the PSP-compatible to PGF font format. Using the font mod/hack released by TeamOverlord, FreePlay, and Skylark a few days ago, you can now change your PSP's font to a font of your choice on all PSP firmwares, truely making your PSP unique to 'normal' PSPs. Although the font mod/hack was originally intended to open up exploitations on the PSP firmware (although that is still not out of question), they decided that this would also be a cool customization to release to the public, and indeed, it is definitely a nice mod. The new TTF to PGF font converter released today now opens the capability of using thousands of Windows fonts on your PSP, from such places as dafont.com, or from your /WINDOWS/Fonts/ folder on your hard drive. Great work guys!