Bernard Flach and myself have written a modification for wordpress that enables you to add enclosure information to your posts. This info will generate an enclosure-tag in the rss 2.0 feed.
You can download the mod here: http://www.ipportunities.nl/wordpress/index.php?p=49
For more information what you can do with enclosures take a look at: http://www.ipodder.org
Greetz, Pieter & Bernard