If you need to get the Mouse Position at any time in WinForms, you can use:
Point currentPoint = MousePosition;
That will return where the Mouse is in screen co-ordinates.
To get from screen co-ordinates to current Form co-ordinates:
Point currentFormPoint = this.PointToClient(MousePosition)
To get the co-ordinates in a specific Control, like a PictureBox:
Point currentControlPoint = pictureBox1.PointToClient(MousePosition);