We have been working to get more detail in the SDK for Microsoft SharePoint Products and Technologies. To use this additional documentation you have to use the online documentation rather than the downloaded WSS SSDK and the MOSS SDK.
We will also work to get this included in the downloaded SDK, and we will keep working on getting more detail in the SDK, for now here's a list of the new material so far. Scroll down to the "Community Content" in each article to see the new detail.
Hope this helps