Here is a curiousity question. I have an application that must support both flat files and the database as a place to persist data. I was thinking maybe using a .csv or tab-delimited set of files as input ...
Is it possible to use NHibernate to write to do both persistance tasks?
No not to the best of my knowledge. I have the same requirement and have ended up just using flat XML files and hand rolling all the CRUD.
Just today I did happen to notice this File System Database on codeplex but haven't looked into it properly yet.
Try using the Jet engine (see this)
Dialect and other nhibernate settings should be the ones for Microsoft Access.