Many peoples are trying the hard way importing their feed subscriptions to Mail, they wrote a PHP script or importing the RSS to OPML and than load it to Sage extension with Firefox, save it to bookmark..yada yada yada…
I am figuring out the other way around. I found this is the most efficient way to make Mail as my default RSS reader. So, here is what I did to import hundreds of my RSS feed into Leopard Mail.
Open up your RSS reader, I use Vienna. Select the feeds you want to be moved to Mail.

Open up Mail and click the + button on left down corner. Select the Specify a Custom feed URL on Mail popup dialog.

Than drag the feeds from your RSS reader to the box, if you have multiple feeds dragged Mail will automatically break it into different lines. Hit add button. Mail will process your feed, the speed is defend how many feeds you have.

That’s it now you have Mail as your feed reader.