I just recently finished reading the "A Journey with Domain Driven Design (and NHibernate)" series on Ben Scheirman's blog.

• A Journey with NHibernate - Part 1
• A Journey with NHibernate - Part 2
• A Journey with NHibernate (and DDD) - Part 3
• A Journey with Domain Driven Design (and NHibernate) - Part 4
• A Journey with Domain Driven Design (and NHibernate) - Part 5
• A Journey with Domain Driven Design (and NHibernate) - Part 6
• A Journey with Domain Driven Design (and NHibernate) - Part 7
• A Journey with Domain Driven Design (and NHibernate) - Part 8

It is a very good introduction to TDD, NHibernate, DDD, NUnit.

I'm personally trying to learn NHibernate.  I already practice the other items at my current position.

Ayende mentions the above blog and others to help a developer get started with NHibernate.