I also don't understand completely what problem you have ... but perhaps you try the following :
Private Sub Form1_Paint(sender As Object, e As PaintEventArgs) Handles MyBase.Paint
Dim canvas As Graphics = e.Graphics
Dim blackpen1 As Pen = New Pen(Color.Black, 2)
Dim point1 As Point = New Point(210,210)
Dim point2 As Point = New Point(MousePosX, MousePosY)
canvas.DrawLine(blackpen1, point1, point2)
If you use the Graphics-Object out of the Eventargs of the Method you have complete access to the area from the Form.
Perhaps that helps ...