Originally Posted by Drahken
MP4 contains either mpeg4 (of which divx & xvid are variants) or h264. H264 is complex, with a high overhead, not everything that supports mp4 will support h264 (and even if it technically does, it will require a lot of processor power & ram). Anything which supports mp4 is guaranteed to support basic mpeg4 though.
I have seen quite a few vids available in mp4 downloads recently. We can't give you any links to such files or places to get such files though.
SUPER can convert almost any format to almost any other format. It can convert from/to mkv & ogm, and has presets for converting to psp & ipod compatible mp4.
Mediacoder likewise can convert to/from almost any formats, and has presets for psp & ipod. Mediacoder is the more powerful of the 2, but is also less userfriendly. The choice between mediacoder & SUPER comes down to a choice between power/control & ease of use.
SUPER is also compatible with avisynth which makes it quite appealing to the mid level user.
xvid4psp isn't a very powerful tool but you'll have to settle for it if you don't know basic command line.