I assume you're trying to system link? You didn't say which games you'd be playing but some games may only support a certain number of players on a splitscreen (1, 2, or 4), so keep that in mind.
So for example, if you were playing Halo 3 (supports 4 players per screen) with 16 people you'd need 4 Xbox 360's, 4 different displays, 16 controllers and someway to connect all 4 Xbox 360's in a network. You can either buy four wireless adapters or a bunch of ethernet cables.