  In this paper, we study the Drinfeld cusp forms for $\Gamma_1(T)$ and
$\Gamma(T)$ using Teitelbaum's interpretation as harmonic cocycles. We obtain
explicit eigenvalues of Hecke operators associated to degree one prime ideals
acting on the cusp forms for $\Gamma_1(T)$ of small weights and conclude that
these Hecke operators are simultaneously diagonalizable. We also show that the
Hecke operators are not diagonalizable in general for $\Gamma_1(T)$ of large
weights, and not for $\Gamma(T)$ even of small weights. The Hecke eigenvalues
on cusp forms for $\Gamma(T)$ with small weights are determined and the
eigenspaces characterized.
