Windows Vista does not have DOS, the command line you get from cmd.exe is not a DOS prompt, so any DOS based applications won't work natively on that OS. To run DOS games on a modern system you need to get a program called DOSBox. You can get it free at DOSBox.com. It is a DOS emulator that will allow you to run most DOS titles. What you do is mount the directory containing the troika.exe file as the c drive in DOSBox, then just type in the name of the exe, hit enter and it should work.