P-GRADE, a graphical tool and programming environment was used to parallelize atomic level reaction dynamics codes. In the reported case study a classical trajectory code written in FORTRAN has been parallelized. The selected level was coarse grain parallelization. PGRADE allowed us to use automatic schemes, out of which the task farm was selected. The FORTRAN code was separated into an input/output and a working section. The former, enhanced by a data transfer section operates on the master, the latter on the slaves. Small sections for data transfer were written in C language. The P-GRADE environment offers a user-friendly way of monitoring the efficiency of the parallelization. On a 20-processor NPACI Rocks cluster the speed-up is 99 percent proportional to the number of processors.