Awesome. =)
If you know the name of a process to kill, for example notepad.exe, use the following command from a command prompt to end it:
taskkill /IM notepad.exe
This will cause the program to terminate gracefully, asking for confirmation if there are unsaved changes. To forcefully kill the same process, add the /F option to the command line. Be careful with the /F option as it will terminate all matching processes without confirmation.
(via XP: kill a Windows process from the command line with taskkill | Windows | Tech-Recipes.)
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