If you want to send keystrokes or mouse events, you want to use Win32::GuiTest.

This usually conflicts with processes started through a service though, becuase Windows permissions disallow sending events from processes started through a service to the desktop (or so I think).

If you want to launch a process from the outside, either have an SSH daemon running on the target machine or use WMI (if you are Administrator in your domain) or write a small HTTP server that then launches the target process.