  So far, quantum properties of N=1/2 nonanticommutative (NAC) super
Yang--Mills theories have been investigated in the WZ gauge. The gauge
independence of the results requires assuming that at the quantum level
supergauge invariance is not broken by nonanticommutative geometry. In this
paper we use an alternative approach which allows studying these theories in a
manifestly gauge independent superspace setup. This is accomplished by
generalizing the background field method to the NAC case, by moving to a
momentum superspace where star products are treated as exponential factors and
by developing momentum supergraph techniques. We compute the one--loop gauge
effective action for NAC U(N) gauge theories with matter in the adjoint
representation. Despite the appearance of divergent contributions which break
(super)gauge invariance, we prove that the effective action at this order is
indeed invariant.
