I can finally post!
As I said in PSP Linux web, I'm not a programmer, but I can test and
find interesting thigs.
Here I post a download link to a sample to use 720x480 resolution on
PSP.
http://dl.qj.net/psp/homebrew-applications/fullscreen-tv-out-for-homebrew.html
It works only for tv out (component and scart).
Source and binary are included.