Create a tool that allows the user to click the map. In the button click event on your form, get a reference to this tool from IDocument::CommandBars and set it to be the current tool. When implementing your tool, create a custom event called OnPointClicked or something like that. Create a custom event arguments class that contains an IPoint reference as one of its properties. Your custom event should use this custom arguments class for its arguments. In the custom tool's MouseDown event, create a new instance of the custom arguments class, set the point property to be the point clicked and raise the event. In the button click event on your form, register for this event before setting the custom tool to be the current tool. Wire the event to a method on your form that will do whatever you need to do with the point.
