Giovanni,
There isn't an embedded web server on the FP-1601, so you won't be able to use the FP-20xx solution. There currently is not a way to programmatically determine the serial number for a FP-1601. However, you can retrieve the serial number in Measurement & Automation Explorer (MAX). The Knowledge Base below describes how to do it in both MAX and FieldPoint Explorer:
http://digital.ni.com/public.nsf/websearch/4DC33667E86CF99786256C0500582172?OpenDocument
Ames
Applications Engineering
National Instruments