I would simply restrict character entry to zeroes and ones as the user enters them, and limit the length. You'll have to adjust this code for the proper If
checks; I'm a C# guy, not a VB guy.
Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
If e.KeyChar <> ChrW(Keys.Back) Then
If Textbox1.Length < 3 and (e.KeyChar = "0" or e.KeyChar = "1") Then
Else
e.Handled = True
End If
End If
End Sub