Atoms moving in an intense, near resonant standing wave (SW) experience a force along the direction of the SW. This force has been investigated by observing its effect on the transverse velocities of atoms in a thermal beam. When the standing wave is tuned above resonance the atomic beam is collimated and has an increased intensity at the center of the beam. Below resonance, the SW anti-collimates the atomic beam, reducing the central intensity. These effects are due to the interaction between the induced atomic dipole and the inhomogeneous field of the SW. Further investigation shows structure in the transverse velocity distribution of the atomic beam. This structure is due to multiphoton (Doppleron) resonances in the force. Calculations reproduce the dipole force and multiphoton resonance effects and are in good agreement with the data.