  The interaction of surface acoustic waves (SAW) with $p$-type
Si/Si$_{0.87}$Ge$_{0.13}$ heterostructures has been studied for SAW frequencies
of 30-300 MHz. For temperatures in the range 0.7$<T<$1.6 K and magnetic fields
up to 7 T, the SAW attenuation coefficient $\Gamma$ and velocity change $\Delta
V /V$ were found to oscillate with filling factor. Both the real $\sigma_1$ and
imaginary $\sigma_2$ components of the high-frequency conductivity have been
determined and compared with quasi-dc magnetoresistance measurements at
temperatures down to 33 mK. By analyzing the ratio of $\sigma_1$ to $\sigma_2$,
carrier localization can be followed as a function of temperature and magnetic
field. At $T$=0.7 K, the variations of $\Gamma$, $\Delta V /V$ and $\sigma_1$
with SAW intensity have been studied and can be explained by heating of the two
dimensional hole gas by the SAW electric field. Energy relaxation is found to
be dominated by acoustic phonon deformation potential scattering with weak
screening.
