There are 2 things you have to be aware of:
1. The PSP will playback files that have been recorded with the QVGA or WQVGA resolution on the Economy or Normal Settings only. (Fine and Suerpfine will not work, it is a hardware limitation on the PSP side).
2. If you don't have the last PSP firmware (2.

, the files have to be in a specific folder with a specific file structure. Just format your card with your PSP, set the recording resolution to QVGA Normal and you should see the files on your PSP right away. If you install the new firmware (2.

file names and folder structures are apprently no longer an issue.
FJ