How you do it depends upon whether you just need serial input/output, or if you need some random access to the data. If you need random access to the data, then as Ancient Dragon said, you need support for files >4GB (maximum a 32-bit offset can handle. Current Linux systems support access to very large files, for both 32-bit and 64-bit systems by defining the type fpos_t appropriately.
For Each ctrl As Control In Me.Controls("pnlMainPanel").Controls
If ctrl.GetType Is GetType(System.Windows.Forms.Panel) Then
For Each subCtrl As Control In ctrl.Controls
If subCtrl.GetType Is GetType(System.Windows.Forms.TextBox) Then
If subCtrl.GetType Is ...