Format your card if you havent done it and hook it up to your pc or mac. There should be 4 folders, “game”, “music”, “photos”, and “savedata”. In order to put your videos on your psp you need to create a new folder in the root folder (E:\) named MP_ROOT (So it should be E:\MP_ROOT\. Then create another file in MP_ROOT called 100MNV01. So it should be E:\MP_ROOT\100MNV01 (100MNV01 Folder is where you put your video in)
I recommend you using iPSP, Its for Mac useres ONLY!
Download 3gp Converter
Also Download QuickTime(It comes with iTunes)(You have to download by force)(If you have an older version of quicktime, i suggest you still download it.)
Unzip Your 3gp and run setup. You may see some werid letter but its japanese, all you have to do is select English button at the bottom.
After installing run 3gp converter, you may see japanese charecters so all you have to do is go down and select english, if i donsn't have the english button, go open up your 3gp converter file, open up 3gp_converter.ini and set Languages= 0 to Languages= 1. After that select Customized: MP4, for PSP (Direct, renamed) then press apply.
Then choose the video quality you want, i personally put QVGA/19fps/512kbps Stereo/96kbps, dont know if thats any good but i like it. After choosing the quality select the output directory but clicking on select.
Just drag and drop your video into the 3gp convert and it wil converter automatically. After fiinishing converting just drag and drop your video to E:\MP_ROOT\100MNV01 .