Ferromagnetism in dilute magnetic semiconducting oxide materials has attracted both interest and controversy. Most studies thus far have focused on bulk magnetic properties, and the nature of correlations in these materials is therefore poorly understood. Following a polarised neutron scattering study of the spin correlation in lightly doped Mn doped ZnO, which showed that ferromagnetic correlations in Mn:ZnO do not come from a substitution of the zinc by manganese in the ZnO matrix, we propose here an extension of the study to the Co-doped case, in order to clarify the nature of ferromagnetic correlations in Co:ZnO.