Try this:
e.Graphics.Clear(SystemColors.Control);
e.Graphics.DrawString("Normal text", this.Font, SystemBrushes.ControlText, 10, 10);
e.Graphics.RotateTransform(90);
e.Graphics.DrawString("Tilted text", this.Font, SystemBrushes.ControlText, 10, -40);
By default the coordinate system has its origo in the top left corner of the surface, so that is the axis around which RotateTransform will rotate the surface.