Is it possible to do reverse Engineering from a database schema to Classes and (most important) hbm.xml files? I know it can be done with Hibernate, but as I use .NET, it really help to have a way to automatically write the mapping files...

There are several tools/scripts to do this. One place to start is by looking at K-Dub's script for MyGeneration (go to MyGeneration's web site). We started out with that one, although we had to essentially rewrite it after making so many mods. Still, it is a good place to start out.

My favorite is Codus - http://www.adapdev.com/codus/

It is simple and easy to control! I took the beta-version (v1.3.0.0 beta) which you can download from the page... worked well for me! :) It also generates you all the needed classes with easy access-methods and so on... for all the features have a look at the documentation! :)

I downloaded and installed Codus... I might not have to program anything at all!!!

Have you tried ActiveRecord from the Castle project http://www.castleproject.org/index.php/Main_Page

Using ActiveRecord you do not need to write XML mapping files but decorate your classes with attributes and ActiveRecord will do the rest, it uses NHibernate internally for persistence.

It also contains a ActiveRecordGenerator that can generate the attribute decorated classes for you from the DB.

I asked earlier if there were tools for reverse engineering for NHibernate, and some people mentioned a few. One of them seemed particularly helpfull, "Codus", but it has the problem that it makes poor hbm.xml files, because it does not map one-to-many, many-to-one nor many-to-many collections. Besides that, it generated classes inside a class only as an id (instead of an actual object); ie: class "State" has as a variable an object of type class "Country". But Codus generates a class "State" with a property "IdCountry", because that's what there is in the database.
I tryed to do the same in Hibernate (the java version) with a plugin for Eclipse that I think cames with Hibernate, and it DID generate the class "State" with a class "Country" inside... so, the question is... is there a reverse engineering tool for NHibernate that works as the plugin for Eclipse?