Hi, getting deeper into the "Italian job" we must say that here in Italy, professional VAT number is called "Partita IVA", that's a numeric 11 digits string without IT prefix. Italian VAT is made by the described algorithm I can translate for you. http://it.wikipedia.org/wiki/Partita_IVA

Then We have the "Codice Fiscale" (that's a tax id) generally is based on registry data (birthday, birthplace, name and surname) but in some rare cases it must be recalculated.. We have a bunch of "Li Wu" Chinese people Italian citizens but "Codice Fiscale" asks for 6 characters based on name and surname... But this is another problem.
http://it.wikipedia.org/wiki/Codice_Fiscale

The real problem is that since this year (2008) "Codice Fiscale" is also asked and it's required for professionals for each transaction.

ATM I'm just adding a Bio profile with cck fields; there isn't a real validation but using tokens module i'm exposing that fields to UC invoices. And the dirt job is done.