  We derive the transport equations for two-dimensional electron systems with
spin-orbit interaction and short-range spin-independent disorder. In the limit
of slow spatial variations of the electron distribution we obtain coupled
diffusion equations for the electron density and spin. Using these equations we
calculate electric-field induced spin accumulation in a finite-size sample for
arbitrary ratio between spin-orbit energy splitting and elastic scattering
rate. We demonstrate that the spin-Hall conductivity vanishes in an infinite
system independent of this ratio.
