  Extreme ultraviolet (EUV, 13.6 eV $< h\nu \lta 100$ eV) and X-rays in the
0.1-2 keV band can heat the surfaces of disks around young, low mass stars to
thousands of degrees and ionize species with ionization potentials greater than
13.6 eV. Shocks generated by protostellar winds can also heat and ionize the
same species close to the star/disk system. These processes produce diagnostic
lines (e.g., [NeII] 12.8 $\mu$m and [OI] 6300 \AA) that we model as functions
of key parameters such as EUV luminosity and spectral shape, X-ray luminosity
and spectral shape, and wind mass loss rate and shock speed. Comparing our
models with observations, we conclude that either internal shocks in the winds
or X-rays incident on the disk surfaces often produce the observed [NeII] line,
although there are cases where EUV may dominate. Shocks created by the oblique
interaction of winds with disks are unlikely [NeII] sources because these
shocks are too weak to ionize Ne. Even if [NeII] is mainly produced by X-rays
or internal wind shocks, the neon observations typically place upper limits of
$\lta 10^{42}$ s$^{-1}$ on the EUV photon luminosity of these young low mass
stars. The observed [OI] 6300 \AA line has both a low velocity component (LVC)
and a high velocity component. The latter likely arises in internal wind
shocks. For the former we find that X-rays likely produce more [OI] luminosity
than either the EUV layer, the transition layer between the EUV and X-ray
layer, or the shear layer where the protostellar wind shocks and entrains disk
material in a radial flow across the surface of the disk. Our soft X-ray models
produce [OI] LVCs with luminosities up to $10^{-4}$ L$_\odot$, but may not be
able to explain the most luminous LVCs.
