>I'm having trouble doing something pretty basic:
>
>I want to have a form with two buttons on it: Start and Stop
>
>When one pushes 'Start', a background process starts that performs a continuous loop, looking for files in a particular directory, and copying them to another if they exist. In order to stop this sentinel process, one would press 'stop'.
>
>However I write the code, the focus seems to remain with the background endless loop, and I can't get the 'stop' button to work.

As others have said - use a timer - if you don't your 'cancel" interupt may never be heard.