I've found 4 functions with start "Peek" (and they was found at win32.hlp, that you could find with google), that are:
Searching on msdn will give you the required information, hope it helps =).
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 ...