With the release of SharePoint SP1, the team updated the SDK Documentation to reflect the changes. There is an online version only for the time being and you can find it at:

Windows SharePoint Services 3.0 SDK (December 2007 Refresh)

Office SharePoint Server 2007 SDK (December 2007 Refresh)

It should be made downloadable soon and hopefully they are going to axe the BDC Editor requirement on SQL Express. Or even better, let us choose which instance to use as I am tired of having 3 additional instances of SQL Express in addition to my SQL Developer instance.