Each cassette tape and a workbook could be delivered very easily using Real Audio and printable PDF files. One cassette tape would be roughly (very roughly) a 5 megabyte sound file that could be streamed or packaged to be downloaded to the individuals hard drive. A series of multi-followup autoresponders could be initiated to deliver the announcement of each segment and provide your customers with time limited special offers related to your product. This would allow a "hands free" delivery method, and you could easily plug thousands of people into the system as they were ready.
I am assuming you may have considered this -- and for some reason dismissed this idea. I would be interested in hearing why you may not consider this a preferable delivery method. Is there a flaw?
Best Regards, Steve MacLellan
homebusiness-websites.com