This is the second article (and the central piece) about creating add-ins for the VBA editor of Microsoft Office (even the 64-bit edition) using the .NET Framework 2.0 or higher:

HOWTO: Create an add-in for the VBA editor (32-bit or 64-bit) of Office with Visual Studio .NET.
http://www.mztools.com/articles/2012/MZ2012013.aspx