  Yang-Mills theory with a symmetry algebra that is the semidirect product
$\mathfrak{h}\ltimes\mathfrak{h}^*$ defined by the coadjoint action of a Lie
algebra $\mathfrak{h}$ on its dual $\mathfrak{h}^*$ is studied. The gauge group
is the semidirect product ${\rm G}_{\mathfrak{h}}\ltimes{\mathfrak{h}^*}$, a
noncompact group given by the coadjoint action on $\mathfrak{h}^*$ of the Lie
group ${\rm G}_{\mathfrak{h}}$ of $\mathfrak{h}$. For $\mathfrak{h}$ simple, a
method to construct the self-antiself dual instantons of the theory and their
gauge non\-equivalent deformations is presented. Every ${\rm
G}_{\mathfrak{h}}\ltimes{\mathfrak{h}^*}$ instanton has an embedded ${\rm
G}_{\mathfrak{h}}$ instanton with the same instanton charge, in terms of which
the construction is realized. As an
example,$\mathfrak{h}=\mathfrak{s}\mathfrak{u}(2)$ and instanton charge one is
considered. The gauge group is in this case $SU(2)\ltimes{\bf R}^3$. Explicit
expressions for the selfdual connection, the zero modes and the metric and
complex structures of the moduli space are given.
