FYI - I was reading ScottGu's blog this morning and he listed LLBLGen in his latest post about LINQ. Here's the quote:

3) It is extensible and allows any type of data provider to be used with it. For example: an existing ORM engine like NHibernate or LLBLGen could implement the LINQ standard query operators to enable LINQ queries against their existing ORM implementation and mapping engines.