The structure of Fe[x] - Pd[1-x] (0.85 > x > 0.5) and Fe[x] - Pt[1-x] (0.85 > x > 0.3) thin film alloys co-deposited from the vapour phase over substrate temperatures (T[s]) ranging over 200-700°C have been examined at room temperature, using X-Ray, Microprobe, TEM and SEM techniques. The sequence of phases developed as T[s] is changed have been explained in terms of three factors: a) The structure of the initial phase, which in turn is a function of the T[o] temperature where DeltaG[bcc-fcc]=0 b) Diffusion at the designated temperature, which depends on both T[s] and the rate of deposition. c) Further transformations which occur on cooling through critical ordering or martensite start temperatures. Based on the co-deposited thin film results, a model is proposed which facilitates the determination of alloy phase diagrams. A direct determination of T[o] temperature in certain composition ranges is also possible through vapour deposition techniques. Preliminary calculation of T[o] confirms the experimental results and the role played by magnetic contributions. The combined experimental data for Fe-Pt alloys confirm the earlier assumption of a eutectoid transformation at about 17at% Pt at around 600°C and provides evidence of the efficacy of thin films for the rapid assessment of low temperature equilibria.