No, that's not a peizo speaker, just a normal low fidelity paper cone speaker. I have no experience working with piezo speakers, but from what I just read, they have a tendancy to have high capacitive reactance which can be bad in amplifier circuits.
Like I said, there is no guarantee that this circuit will work, It's just a similar design to a circuit I experimented with, with a photoresistor instead of the IR detector.
Q3 is meant to represent the IR detector. D1 is the IR LED. Using a cheapy cone speaker from radioshack this circuit should give you an alternating tone, maybe not a pure two tone, but close.
I'll tell you what, let me pick up the LED and phototransistor, and I'll breadboard it this weekend and ill let you know if it works.