GliGli released a libXenon a Nintendo64 emulator for the homebrew 360. From the Readme/NFO:

Description
Mupen64-360 is a Nintendo64 emulator for the Xbox 360, it's powered by libxenon and it's a port of Wii64 (which itself was a port of Mupen64).

History
v0.96 Beta: First binary release

Credits
Wii64 / Mupen64 teams (guess why :)
GliGli (Xbox 360 port)
Ced2911 (GUI library)
Razkar (Backgrounds)
Everyone that contributed to libxenon...
Homepage:http://libxenon.org/index.php?topic=180.0
Download:http://bayfiles.com/file/14ih/hZTBXL..._v0.96beta.rar