The typical method of accessing Volume Shadow Copy functionality is to use the WMI classes (listed below) but if you are a hardware vendor or just like writing device drivers then you will want access to the direct Win32 calls and I just tracked down the process to get the SDK for the Volume Shadow Copy API's; specifically the calls in vssapi.dll such as:
And thought i should do a blog entry as the task wouldn't have been easy without the ability to see who at Microsoft owned this dll (Turned out it was the very helpful Keith Hageman http://msdn.microsoft.com/chats/transcripts/enterprise/windows_081804.aspx)
The original method was to send email to email@example.com and request a copy which still works and "If" you know the VSSAPI email address( i just did a search and it came up only 6 times on the whole internet i.e. NOT very well known). The new method which is much easier and more discoverable which is to sign up for membership at: www.microsoftstoragepartners.com
Hope this helps somebody!