Since the premium content is not delivered as a podcast, there are a few steps to take to ensure that you can use the premium content in iTunes and subsequently on your iPod.
1. Create a folder on your computer, eg. in My Documents or equivalent. Call this folder "Radio Lingua" or "Coffee Break Spanish" or whatever suits. You can store all your Radio Lingua content in this folder, and you'll soon get used to our naming system, eg. cbs-01-guide.pdf is the pdf guide for lesson 01 of Coffee Break Spanish, etc.
2. Go to the appropriate premium members' page for whichever subscription(s) you have purchased.
3. Control-click (Mac) or right-click (PC) on any of the files and choose "Save as..." or "Download to..." or equivalent.
4. You'll be asked for your username and password. Please ensure that you enter your username in lower case and your password as case sensitive.
5. In the dialog box, navigate to the folder you have created within My Documents in step 1 above.
6. Save the file in this folder.
7. If you wish to transfer the files to iTunes / iPod, then you should now create a playlist in iTunes (File menu > New Playlist), giving it an appropriate name, eg. Coffee Break French, Show Time Spanish, etc.
8. Drag the file from your desktop/Finder into this playlist within iTunes.
9. You can now sync your iPod with iTunes. You may need to ensure that iTunes is set to sync this particular playlist when syncing.
10. Note that the files will not appear in the podcasts section of your iPod. This is restricted to only content which has been downloaded through the iTunes podcast system. Instead, you can access your content through the Playlists area on your iPod.