I don't have any elaborate advice on this, other than create a few blog posts using the UI then study how the data is formatted in the mp_Blog* tables as well as the mp_FriendlyUrls table, and try to import your data so it is formatted the same.
I have a to do in the project tracker to implement support for importing from rss feeds and eventually will get to that but not sure when, unfortuantely not very soon due to other priorities that I'm focused on.
Hope that helps,
Joe