This should get you started:
[VB]
Dim startpoint As Point
Private Sub Form1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles MyBase.MouseDown
startpoint.X = e.X
startpoint.Y = e.Y
End Sub
Private Sub Form1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles MyBase.MouseMove
If e.Button = MouseButtons.Left Then
Dim g As Graphics = Me.CreateGraphics
g.Clear(Me.BackColor)
g.DrawLine(Pens.Black, startpoint, New Point(e.X, e.Y))
g.Dispose()
End If
End Sub
Private Sub Form1_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles MyBase.MouseUp
Dim g As Graphics = Me.CreateGraphics
g.Clear(Me.BackColor)
g.Dispose()
End Sub
[/VB]