All three languages are fine for simulation. C has the least overhead, C++ is the most common in the industry, C# is good if you like C#. mdrand's suggestion of Matlab is also good, if your interest is in finance rather than programming, it will save you time. Matlab is the most common tool for quants.Break this project into two parts. First, code a Monte Carlo simulation of the Libor market model, then worry about pricing FRA's. Both of these projects are straightforward.