  We present infrared ab-plane conductivity data for the layered cobaltate
Na$_x$CoO$_2$ at three different doping levels ($x=0.25, 0.50$, and 0.75). The
Drude weight increases monotonically with hole doping, $1-x$. At the lowest
hole doping level $x$=0.75 the system resembles the normal state of underdoped
cuprate superconductors with a scattering rate that varies linearly with
frequency and temperature and there is an onset of scattering by a bosonic mode
at 600 \cm. Two higher hole doped samples ($x=0.50$ and 0.25) show two
different-size gaps (110 \cm and 200 \cm, respectively) in the optical
conductivities at low temperatures and become insulators. The spectral weights
lost in the gap region of 0.50 and 0.25 samples are shifted to prominent peaks
at 200 \cm and 800 \cm, respectively. We propose that the two gapped states of
the two higher hole doped samples ($x$=0.50 and 0.25) are pinned charge ordered
states.
