Well this is a dodgy example which will answer that question (until someone posts a nicer method of not allowing a textbox selection to be performed):
Code:
Private Sub TextBox1_MouseMove(ByVal sender As Object, _
ByVal e As System.Windows.Forms.MouseEventArgs) Handles TextBox1.MouseMove
Cursor = Cursors.No
Me.TextBox1.SelectionStart = 0
Me.TextBox1.SelectionLength = 1
End Sub
Private Sub TextBox1_MouseLeave(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles TextBox1.MouseLeave
Cursor = Cursors.Default
End Sub