I'm not sure if this applies to your plug-in situation, but I just installed podPress and under its general settings, it explains about premium content. Hope this helps (I'm still a bit confused but I'm sure it'll make sense any day now).
Premium Content (?)
Enable Premium Content: /__/
(?) This is an optional feature which is used to protect some content from being accessed unless users have the appropriate rights. It should NOT be in a dir under your web root. It should be a dir outside of the web root so that users cannot simply browse to the dir and get access to the files.
For example this could be ... /home/premium_mp3s/
Digest auth is MUCH better than Basic, which is easily unencrypted.
Use fake enclosure:
If you want the enclosure to always exist (so feed will show up in iTunes), then check this.
Full documentation is still under development on the wiki
This is the short of it is that you need to get and install the Role Manager plugin
Anyone that should have access to the premium podcasting files need to have the Premium Content role, which can be done by making them Premium Subscribers
Then just in each post set the media file as premium content and normal visitors will not be able to see the content via the web or from the feed.
If your using WordPress 2.1, then users can just use http://www.yoursite.com/?feed=premium for their premium content needs.
If your using WP 1.5 or 2.0.x, then you need to put premiumcast.php in your main wordpress dir and then have your subscribers use this file as their rss feed.
These will cause the site to ask for their user/pass before giving the RSS feed. Juice and iTunes supports this fine.
Keep in mine, that this does NOT protect your content if someone discovers the URLS, it only hides the location from showing up on the site or in the feed. To fully protect your files I have also been able to get this working with aMemberPro
aMemberPro will protect the files from being downloaded at all, unless authorized. It also handles monthly subscription issues thru paypal and such. Its a great tool, and combines with WordPress and podPress you can have a full blown premium content podcasting service.