This question has been asked many times in many forums but I haven't seen a confident conclusive answer. So I'll try my luck again.
I want to know whether and how is it possible to use MySQL as the persistence node (configuration and content) for SharePoint. As of now, I am only interested to know about WSS (I guess same would apply to MOSS as well).
Basically I should be able to define lists, document libraries and all content that lives in MySQL.
My front end will be pure ASP.Net and will use WSS APIs.
The answer is most likely to be "NO". When you install WSS, it will ask for a Microsoft SQL server and will not allow you to choose other kinds of SQL servers.
WSS/MOSS depends on hundreds of inter-related stored procedures living in Microsoft SQL Server, these are quite technology specific and use Microsoft SQL- only solutions in there.
However, if you do not want to pay for MSSQL Server, you can install WSS/MOSS on Microsoft SQL Express edition, this works fine, except you have size limit of 4GB.