MSDN has a nice URL mechanism to reference several Visual Studio versions of the same documentation, for example:

Automation and Extensibility for Visual Studio (Visual Studio 2010)
http://msdn2.microsoft.com/en-us/library/xc52cke4(en-US,VS.100).aspx

Automation and Extensibility for Visual Studio (Visual Studio 2008)
http://msdn2.microsoft.com/en-us/library/xc52cke4(en-US,VS.90).aspx

Automation and Extensibility for Visual Studio (Visual Studio 2005)
http://msdn2.microsoft.com/en-us/library/xc52cke4(en-US,VS.80).aspx

Long overdue, but today I have updated the MZ-Tools Resources about Visual Studio .NET extensibility page with links to Visual Studio 2010 extensibility resources (downloads of SDKs, documentation, etc.).