  A study is presented of a two-dimensional frustrated and dimerized quantum
spin-system which models the effect of inter-chain coupling in a spin-Peierls
compound. Employing a bond-boson method to account for quantum disorder in the
ground state the elementary excitations are evaluated in terms of gapful
triplet modes. Results for the ground state energy and the spin gap are
discussed. The triplet dispersion is found to be in excellent agreement with
inelastic neutron scattering data in the dimerized phase of the spin-Peierls
compound CuGeO_3. Moreover, consistent with these neutron scattering
experiments, the low-temperature dynamic structure factor exhibits a
high-energy continuum split off from the elementary triplet mode.
