Hi,

There is no need for the EventDispatcher. You just assign the function to the relevant onRelease properties.

Code:
import mx.utils.Delegate;

class main_movie extends MovieClip
{
    public var pbSend:Button;
    public var my_mc:MovieClip;
    public var my_button:MovieClip;

    // constructor
    public function main_movie()
    {
        my_mc = attachMovie ("my_mc", "my_mc", getNextHighestDepth(), {_x :100, _y:50} );
        my_button = attachMovie ("my_button", "my_button", getNextHighestDepth(), {_x :100, _y:50} );
        my_button._x = 100;
    }

    // I would rather do it here...
    private function onLoad ()
    {
        my_mc.onRelease = my_button.onRelease = Delegate.create(this, checkFields);
    }

    private function checkFields():Void
    {
            trace("check");
    }
}