im not sure if it has been answered yet but to put your mp3's from your comp on you gta game go here and download it
ok now plug your psp in go to psp gamesaves and make a new folder called
now that youve done that open up EAC psp edition and browse for the music you want to convert
make sure you select transfer to hard disk not psp.
when you save them i usually save them to a folder on my desktop called psp music transfer them into your folder ULUS10041CUSTOMTRACKS
now before your done rename them to .gta EX: gtalcsrocks.gta and then boot up gta lcs and hit start audio and enable custom soundtracks
im sure ive helped many headaches