  We discuss the properties of semiconducting bulk ZnO when substituted with
the magnetic transition metal ions Mn and Co, with substituent fraction ranging
from $x$ = 0.02 to $x$ = 0.15. The magnetic properties were measured as a
function of magnetic field and temperature and we find no evidence for magnetic
ordering in these systems down to $T$ = 2 K. The magnetization can be fit by
the sum of a Curie-Weiss term with a Weiss temperature of $\Theta\gg$100 K and
a Curie term. We attribute this behavior to contributions from both \textit{t}M
ions with \textit{t}M nearest neighbors and from isolated spins. This
particular functional form for the susceptibility is used to explain why no
ordering is observed in \textit{t}M substituted ZnO samples despite the large
values of the Weiss temperature. We also discuss in detail the methods we used
to minimize any impurity contributions to the magnetic signal.
