A quantum-mechanical procedure is described for calculating the ro-vibrational states of weakly bound molecular clusters using a basis function approach. The method involves using a body fixed Jacobi-type coordinate system, which provides an orthogonal kinetic-energy operator. The evaluation of all angular degrees of freedom is performed analytically through a suitable expansion of the potential. The radial degrees of freedom are treated numerically with a discrete variable representation. The approach is applied to the (H-2)(2) and (H-2)(3) systems treating the H-2 monomers as rigid bodies. For zero total angular momentum, it is found that (H-2)(3) has only one bound-state for each symmetry, with the ortho-ortho-ortho symmetry being the most stable.