  A linear theory of electron transport is developed for a system of two ideal
quantum wires, of length L, coupled by tunneling and Coulomb interaction. The
interaction of electrons with acoustical phonons is included and the results
are valid in both the ballistic and diffusive regime. In the {\it ballistic}
regime, both tunneling and Coulomb drag lead to a {\it negative}
transresistance R_{TR}, while in the {\it diffusive} regime the tunneling
opposes the drag and leads to a {\it positive} R_{TR}. If L is smaller than the
phase-breaking length, the tunneling leads to interference oscillations of the
resistance that are damped exponentially with L.
