NHibernateEg may be a good start:
http://nhibernate.sourceforge.net/NHibernateEg/
Note that the mapping with .NET attributes is similar with the mapping with XML; so if you read a mapping done in XML, you should be able to easily convert it in .NET attributes.
Here is a page refering to most articles/tutorials/samples/tools available on NHibernate:
http://hibernate.org/365.html
And don't forget the official documentation of NHibernate.Mapping.Attributes:
http://www.hibernate.org/hib_docs/nhibernate/html/mapping-attributes.html (it contains many useful tips...)