>How can I kill an active application in window without user interface.
>
>I am trying to launch a batch process that will kill an application and relaunch it. I am using the registry to relaunch the application but I am not sure how can I determine what is the active running application in the windows?
>
>Would that be API call, registry call, or others.?

You can use the FindWindow and SendMessage API functions to kill an app. Try a search here for some sample code, it has been posted several times.