C#

Pen pen = new Pen(Color.Black, 1);
Point point1 = new Point(0,0);
Point point2 = new Point(10,10);
Graphics graphics = Graphics.FromHdc(this.Handle);
graphics.DrawLine(pen, point1, point2);
graphics.DrawImage(bimap, blah blah blah);
// you can change the color and/or width and do some more drawing

// but then you have to dispose the pen when you're done with it.
pen.Dispose();
// clean up the graphics object too
graphics.Dispose();