OpSim is available from the OpSim website. There are archives available from the download section for different platforms and architectures. OpSim should run out of the box, without installation procedure. To use OpSim, just unpack the archive and run OpSim!
OpSim should run on any computer as long as OpenGL is available. If you have trouble running OpSim then let us know. Running simulations requires a lot of memory and processing power, therefore more powerfull machines will perform better.