One of the topics I have not covered on my DNN Help website is creating providers for DNN. I have created solutions like SingleSignOn that allow you to interface DNN with another website. While this solution may be valid in certain situations, it is not the best solution when you want a tight integration with an external website. Creating your own membership provider is definitely the best way to go.
However, creating your own DNN membership provider is REALLY "getting your hands dirty". It is no wonder most people including myself have avoided it.
I have had the opportunity to see the preview of:
Done in 60 Minutes: Build a Custom Membership Provider by Antonio Chagoury (the session is not listed on the OpenForce website but he will be giving the presentation at OpenForce 08).
In it he will show how simple the process is. What this will give you will be very powerful. You can have total control over the DNN membership process WITHOUT altering the core. This is a "extension point" that is designed for you to implement.
Afterwards you will be able to talk to Antonio in person and perhaps get advice on your particular situation.
This experience alone is worth the price of the conference don't you think?
There is still time to make it to OpenForce 08, see:
http://openforce08.com/Home/OpenForceNorthAmerica/Overview/tabid/128/Default.aspx