I used to work for an "e-mail marketing" company. We did a lot of research and it really isn't neccessary to send both forms of e-mail. 98% of e-mail recipients have HTML preset by Microsoft. They want to SPAM you with HTML e-mail, so they set their e-mail app to accept HTML e-mail.
Most people never even think of turning it off. There is no need for a multipart e-mail.
People used to be more willing to help out around here. What seems to be the problem?
The example given above from the manual is sufficient to get started, but get creative. You'll be surprized at what you can do.
Good luck