Re:
Hello,
You can install programs onto an external hard drive, and run them on your PC. However, if you hook the external drive up to another PC, and run the program, there's a high chance of the program failing to run, or failing to run correctly, because there isn't the same operating system with the same data in the registry required for it to work properly.
Unless the program is standalone and doesn't rely on the registry (for example, media player classic and portable apps like portable firefox) then it probably will not work.