N800 version of MPlayer will not work on 770. Even installing OS2007 on Nokia 770 will not magically add support for missing instructions to its CPU. I believe I have seen some reports about successfully using the latest 770 version of MPlayer with OS2007HE on Nokia 770, that's what you should try (I don't know what problems did the original poster have, not getting even a menu entry is very strange, probably his package manager got broken for some reason and screwed up everything).

What are the ideas about fixing this problem?