Unfortunately, the migration that you are talking about actually requires a customization to the product.
As a sidenote, you must export to html if you want to transfer over your attachments.
I'll keep you posted on our progress here internally to get a migration path in place.
Actually Anthony, I'm pretty sure Simon is right and that you must export to XML, not HTML, in order to carry across the attachments. We are in the process of doing this right now and we have to export to XML