A variational treatment is presented to study bound and quasibound states of X(1)...BC...X(2) van der Waals clusters, where X(1) and X(2) are rare gas atoms and BC is a conventional diatomic molecule. The Hamiltonian operator, including all the degrees of freedom, is expressed in terms of the B-C relative vector and bond coordinates which describe the position of each rare gas atom with respect to the BC center of mass. In a body-fixed reference system, with the Z axis parallel to the diatomic axis, all the matrix elements of the Hamiltonian are evaluated in a basis set of functions which takes into account the symmetries of the system. Numerical applications to the He-2...Cl-2 and Ne-2...I-2 complexes are presented and discussed.