I think the OP is getting at being able to tell if the user has entered a number or not.
One way to do that would be to use the .fail() method of the input stream. You could also probably use stringstreams.
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 ...