Best documentation for Nhibernate or best place to start is reading Java book for Hibernate or Hibernate documentation.
Ayende has some useful posts.
Let me quote from Java Experts first
Richard Conway. JDJ.SYS-CON.COM writes
Hibernate has come a long way since it was first released. It has a bewildering number of options for configuring your object persistence mappings and behavior – as well as great tools to make it if not painless then at least no so painful.
If you want to quickly persist your objects for a small project and you can manage uniqueness and referential integrity within your application code – look no further than DB4O. It just doesn’t get any easier.
The Cache/Jalapeno combination provides a compelling option for quickly persisting your java objects with a minimum of effort while providing excellent control over database-specific functionality.
Bruce A. Tate of Beyond Java book fame writes
Most of us try to learn an object relational mapper, like Hibernate. While it does relieve some of your persistence burdens, it also imposes a steep learning curve.
My Advice for fellow ex-VB6.0 programmers
Go for Code Generation route if you can go
Very soon I am going to write some posts showing O/R mapping examples using Nhibernate Custom Attributes.