1. The user running the program. That's easy to change: login as another user and run the program. Or enable and use "run as" (described in http://support.microsoft.com/kb/294676).
2. A program run with user SYSTEM (like antivirus programs). I think it needs some programming to do so.
3. Local or network services. No need to change those, I'd say.
On Windows Task Manager, on the Processes tab: User Name...how can I change the Owner name?