I had a partner ask me about Office Live today, so these are the places you need to start:

1) Client SDK - Windows Live ID Client 1.0 SDK in Alpha

2) Web Based Info - http://forums.microsoft.com/msdn/showpost.aspx?postid=924592&siteid=1 and http://msdn2.microsoft.com/en-us/office/aa905514.aspx

3) Windows SharePoint v3 APIs - Working with Windows SharePoint Services 3.0 Web Services (what is supported from WSSv3 and what is blocked)

4) Some important sections:

How to: Integrate Access 2007 and Excel 2007 with Office Live
How to: Integrate Office Live with other Office 2007 applications

Chris's unofficial Office Live developer blog

That is it for now - the client SDK is key - you can build rich client applications and then share data via the OfficeLive web.  nice.

ttfn

David