Lei Zhou’s Blog

An introduction telling you how to downgrade any current PSP hardware version (TA-079 - TA-086) from firmware 2.81-3.03 to 1.50:
http://dl.qj.net/Downgrader-for-v3.03-PSP-PSP/pg/12/fid/12431/catid/114

Put the link here, in case I can not found it again.

The only format accepted by psp is MPEG-4. There are two types of MPEG-4 files. Both are named as .MP4. One is MPEG-4, Part2, the other is MPEG-4, Part 10 (ofter also referred as AVC). The difference is discribed here: http://en.wikipedia.org/wiki/Video_codec. If your video already is MP4 format and your PSP firmware version is below V3.0:
1) create a folder named “MP_ROOT” in PSP memory stick
2) inside that folder create an “100MNV01″ folder, and a “100ANV01″ folder.
3) If your video is “MPEG-4, Part2″ format, rename it with this format “M4VXXXXX.MP4″, rename the thumbnail with this format “M4VXXXXX.HTM”, XXXXX are five random numbers you like. Save it in “100MNV01″ folder.
4) If your video is “MPEG-4,Part10″ format, rename it with this format “MAQXXXXX.MP4″, XXXXX are five random numbers you like. Save it in the folder “100ANV01″.

If your PSP firmware version is above V3.0
1) create a folder named “MP_ROOT” in PSP memory stick
2) inside that folder create a “Video” folder
3) then copy your MP4 file to this folder, done

If your video is not MP4 format, you need a video converter to convert it to MP4 format, I recommend ‘PSP Video Suite’ for you, it can rip DVD movie and convert many video formats to PSP format. It also provides a ‘PSP Files Manager’, you needn’t create any folder by yourself. The software will help you transfer files to memory stick. I always use it to enjoy videos on my psp, very easy to use and works perfect for me. Here is step by step guide about this software.
http://www.dvd-ripper-copy.com/forum/viewtopic.php?t=610
You can download it free from here
http://www.dvd-ripper-copy.com/PSP-video-suite.html

Original article can be found here: http://answers.yahoo.com/question/index?qid=20070328150231AAuUJP9