Underneath is usually a very literal term. "She is underneath the table." In that sentence I can also say "She is beneath the table." However, "beneath" can also be used to refer to something of a lower position that is non-physical in nature. "Jobs like this are beneath me." That sounds very snobby, but it's saying that your ranking is too high to do jobs that are trivial or unimportant. If you were to use "underneath" in that sentence it would sound very literal and incorrect.

They are the same.