Il problema mi e' stato risolto cosi':

<%@ Language=VBScript %>
<%
sub DirectoryTree(path)

dim fs, folder, item

set fs = CreateObject("Scripting.FileSystemObject")
set folder = fs.GetFolder(path)

'Display the target folder and info.

Response.Write("" & folder.Name & "")
Response.Write("
" & vbCrLf)

'Display a list of files.

Response.Write("<ul>")
for each item in folder.Files
Response.Write("[*]" & item.Name & "" & vbCrLf)
next
Response.Write("[/list]")

'Display a list of sub folders.

for each item in folder.SubFolders
DirectoryTree(item.Path)
next

end sub

path = Server.MapPath("/virtual_path_dir/")

Call DirectoryTree(path)
%>