Hello, all. Sorry for the stupid question, but is it possible to use the jpamodelgen (the tool for generating the JPA metamodel files) with Hibernate mapping files? Or do I absolutely have to convert everything to annotations? I followed the instructions at the jpamodelgen documentation page, but nothing gets generated.

I don't know for sure, but from the documentation you referenced it looks like it should be able to process JPA mapping files, are you pointing it at a Hibernate mapping file instead?

There's a difference between Hibernate mapping files and JPA mapping files? (Can you blame me for finding this a bit confusing?) Is there anywhere that nicely sums up all the various different Hibernate tools and JPA tools and how they work together?

No I don't blame you at all for being confused; Hibernate predates and heavily inspired JPA, so there is quite a bit of overlap between them.
I don't know of one source that provides a summary of the toolsets sorry. The "Getting Started Guide" at http://www.hibernate.org/docs contains good examples of mapping using Hibernate and JPA, but nothing of substance on tooling.