If you solve the Time Independent Schrödinger equation for the Harmonic Oscillator, that is
[tex]-\frac{\hbar^2}{2m} \frac{d^2\Psi}{dx^2} + \frac{1}{2}kx^2 \Psi = E \Psi[/tex]
The quantization of energy comes from the boundary conditions (ie, [itex]\Psi = 0[/itex] when [itex]x= \infty[/itex] or [itex]x = -\infty[/itex]).
The permitted energy levels will be
[tex]E_n = (n+\frac{1}{2}) \hbar \omega[/tex]
So the lowest Energy is not E=0.