Just looked at a picture of the 4.6 engine on Google (BMW 4.6 V8) and it certainly looks chain driven, the ally castings at the front would all have to be striped off if it were belt. Belts tend to be behind plastic covers and chains behind or rather inside ally castings. You can't rely on that to be universally correct but it's true in 99% of the cases, best to check, any BMW dealer would tell you if their 4.6 V8 requires a belt change, to be totally sure.
