This series of posts is going to be interesting whether you use NHibernate or not as it starts to walk through how you can implement IQueryable on something real (like NHibernate).

I didn't understand some of the NHibernate stuff but I was following the LINQ stuff fine and found it valuable because of that.

The post walks through taking an NHibernate concept, ISession and getting an IQueryable from it by adding an extension called Linq<T> in much the same way as the framework seems to have an AsQueryable today.

It also talks about how the Expression property on that IQueryable is then called followed by CreateQuery.

All good stuff :-)