You would randomly select two Integers, create a Point and assign that to the control's Location property, e.g.
vb.net Code:
Private rand As New Random
Private Sub Timer1_Tick(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Timer1.Tick
Dim clientSize As Size = Me.ClientSize
Me.Label1.Location = New Point(rand.Next(0, clientSize.Width - Me.Label1.Width), _
rand.Next(0, clientSize.Height - Me.Label1.Height))
End Sub