SICURAMENTE esiste un metodo più semplice, rapido e spartano ma al volo mi è venuto in mente questo:
Set FL = fso.GetFolder(percorso)
Set SF = fl.SubFolders
For Each FL in SF
Set FL1 = fso.GetFolder(fl)
Set SF1 = fl1.SubFolders
For Each FL1 in SF1
Set FL2 = fso.GetFolder(fl & "\" & FL1.name)
Set SF2 = fl2.SubFolders

If SF2.count > 0 then
Set FL3 = fso.GetFolder(fl & "\" & FL1.name)
Set SF3 = fl3.SubFolders
For Each FL3 in SF3
For Each whatever in fl3.Files
Nome_File = Trim(LCase(whatever.name))
Next
Next
tfile2.close
set tfile2=nothing
Set FL3 = nothing
Set SF3 = nothing
End if

Next

Next

<%Set Fso = CreateObject("Scripting.FileSystemObject")

percorso=server.mappath(".")

Set FL = fso.GetFolder(percorso)
Set SF = fl.SubFolders
For Each file in fl.Files
'cartella principale
response.write percorso & "\" & file.name & "<br>"
Next

For Each FL in SF
Set FL1 = fso.GetFolder(percorso & "\" & fl.name)
Set SF1 = fl1.SubFolders

For Each file in fl1.Files
'sotto cartelle
response.write percorso & "\" & fl.name & "\" & file.name & "<br>"
Next


Next

Set FL = nothing
Set FL1 = nothing
Set SF = nothing
Set SF1 = nothing
%>