I think I might like the hbm2net tool but can not get it to work. 
Can someone give me a step by step example?
Let's use the User.hbm.xml file from the Quick Start Guide
Code:
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
   <class name="NHibernate.Examples.QuickStart.User, NHibernate.Examples" table="users">
      <id name="Id" column="LogonId" type="String" length="20"> 
         <generator class="assigned" /> 
      </id> 
      <property name="UserName" column= "Name" type="String" length="40"/> 
      <property name="Password" type="String" length="20"/> 
      <property name="EmailAddress" type="String" length="40"/>
      <property name="LastLogon" type="DateTime"/>
   </class>
</hibernate-mapping>