I never saw simplepie before, (bookmarked it now - thanks Dave)
As I said, I don't know wordpress, (something i have yet to get into, can you recommend it ?) and simplepie may be the way to go here, but in general terms, if you have two linked tables, a single recordset may be all you need.
if you want to explore this, let me know the table details and i can help you with the sql