The installer for the LabVIEW run-time engine can be found at \..\National Instruments\LabVIEW 6\AppLibs\installs. You will need separate run-time engines for the PC and Mac as executables are not cross-platform. To run an executable on a PC, you will need to use the PC version of the application builder and to run an executable on a Mac, you will need the Mac application builder. When you get 6.1, if you build an application with it, you will need to install a 6.1 run-time engine.