Lock Text Boxes (VB 2005)

I have a set of Text Boxes on a form that I am trying to lock. They're in various containers on that form however, so I have to do multiple loops to get them all. Is there an easier way to do this?

Here's my code (Thanks to carl_tawn for showing me the CType method):

    Private Sub LockFields(ByVal Lock As Boolean)
        For Each ctrl As Control In Me.SplitContainer2.Panel2.Controls
            If TypeOf ctrl Is TextBox Then
                CType(ctrl, TextBox).ReadOnly = Lock
            End If
        Next
        For Each ctrl As Control In Me.TabPage1.Controls
            If TypeOf ctrl Is TextBox Then
                CType(ctrl, TextBox).ReadOnly = Lock
            End If
        Next
        For Each ctrl As Control In Me.TabPage2.Controls
            If TypeOf ctrl Is TextBox Then
                CType(ctrl, TextBox).ReadOnly = Lock
            End If
        Next
    End Sub