The methods needed to carry out calculations on the bound states of atom-molecule Van der Waals complexes containing atoms in P states are presented. Both close-coupling and helicity decoupling (coupled states) formalisms are described. The anisotropy of the interaction potential and the atomic spin-orbit coupling are fully included. The formalism is also applicable to the scattering of molecules by P-state atoms. The methods are applied to the vibration-rotation energy levels of the Cl-HCl Van der Waals complex. An intermolecular potential for Cl-HCl that is valid at long range is constructed, based on knowledge of the Ar-HCl, Ar-Cl, and Ar-Ar potentials. There are important electrostatic contributions arising from the atomic quadrupole of the Cl atom. Bound-state calculations are performed, using both helicity decoupling and close-coupling calculations. The patterns of bending and stretching vibronic levels and the rotational structure are investigated. The microwave spectrum and the frequencies of the main bands in the far-infrared and mid-infrared spectrum are predicted.