  String compactifications with non-abelian gauge fields localized on D-branes,
with background NSNS and RR 3-form fluxes, and with non-trivial warp factors,
can naturally exist within T-dual versions of type I string theory. We develop
a systematic procedure to construct the effective bosonic Lagrangian of type I
T-dualized along a six-torus, including the coupling to gauge multiplets on
D3-branes and the modifications due to 3-form fluxes. Looking for solutions to
the ten-dimensional equations of motion, we find warped products of Minkowski
space and Ricci-flat internal manifolds. Once the warp factor is neglected, the
resulting no-scale scalar potential of the effective four-dimensional theory
combines those known for 3-form fluxes and for internal Yang-Mills fields and
stabilizes many of the moduli. We perform an explicit comparison of our
expressions to those obtained from N=4 gauged supergravity and find agreement.
We also comment on the possibility to include D9-branes with world-volume gauge
fluxes in the background with 3-form fluxes.
