Based on a scanning near-field optical microscopy apparatus, elastic scattering of surface plasmon polaritons, being excited via the Kretschmann coupling scheme, is investigated. The excitation sources include focused and parallel light from a He-Ne and a Ti:Sapphire (725 to 890nm) laser. Prior to scattering investigations, the surface plasmon polariton intensity profile from a focused excitation beam is studied in detail and its behavior is modelled. The samples consist of 45 to 80nm thick silver and gold films. The gold films contain deposited gold nano-particles arranged as either single scatterers, line arrays or periodic surface plasmon band gap structures with straight channels of missing particles. Modelling of the field intensity distribution is made by means of a multiple scattering dipole approach treating the individual particles as point-like scatterers.