The first PLEED measurements of an ordered two component system (Cu(,3)Au(001)) are reported. Using this data an attempt is made to determine the long range order parameter as a function of the crystal temperature. A polarized electron source with an electron spin polarization of 27% and delivering a current of 0.3(mu)A to the crystal surface is described in the first section. This source uses photoemission from negative electron affinity GaAs(001) to produce an electron beam whose polarization can be easily modulated without changing other characteristics of the beam by changing the helicity of the photoemission light. Once operational, the source is used in an attempt to determine the long range order parameter of the (001) face of Cu(,3)Au. Polarization vs. Energy (P-V) curves were taken at room temperature at a number of angles ((theta)) to obtain usable P-V curves for theoretical modeling. Next, P-V curves were measured for the 00 beam at 13 degrees and the 01 beam at normal incidence as a function of temperature. As the crystal was heated through the order-disorder tranition temperature no large change in the P-V curves was noted.