  We consider the 1-loop effective potential in type I string theory
compactified on a torus, with supersymmetry broken by the Scherk-Schwarz
mechanism. At fixed supersymmetry breaking scale M, and up to exponentially
suppressed terms, we show that the potential admits local minima of arbitrary
sign, in dimension d<=5. While the open string Wilson lines are massive, the
closed string moduli are flat directions. In a T-dual picture, the relevant
backgrounds involve isolated 1/2-branes, whose positions are frozen on
orientifold planes, thus decreasing the rank of the gauge group, and
introducing massless fermions in fundamental representations.
