Newer version of iTunes no longer have the OPML export option.  To add a podcast to Miro, you'd have to select the podcast, copy the url, then you Sidebar - Add Podcast to add it to Miro.

For older version of iTunes

You must be subscribed to a video or audio podcast in iTunes, before you can export it to Miro (use the iTunes music store to find free podcasts).


Once subscribed, open iTunes, click File -> Export.


Choose OPML as the format and then save the file.


Open Miro and click Sidebar > Import Podcasts (OPML).


All of your iTunes podcast subscriptions will be imported to the Miro sidebar.