The next article about creating an add-in for the VBA editor of Office with the .NET Framework, and before writing articles related to the setup, is about creating toolwindows. If you thought it was going to be easy…it’s tricky as hell, with several issues. But fortunately I have found workarounds for all of them:

HOWTO: Create a toolwindow for the VBA editor of Office from an add-in with Visual Studio .NET.
http://www.mztools.com/articles/2012/MZ2012017.aspx