Paul Stubbs, a program manager on the programmability team within the Developer division, has written an interesting article about VSTA that was published in the August 2006 issue.

Here's a link to the article:

http://msdn.microsoft.com/msdnmag/issues/06/08/AddInPower/default.aspx

In his article, Paul does a good job of describing some of the differences between three Microsoft programmability technogies: Visual Basic for Applications (VBA), Visual Studio Tools for Office (VSTO), and Visual Studio Tools for Applications (VSTA).

The article also describes how InfoPath 2007 has integrated VSTA to allow developers to customized the structured data forms that are a key feature of InfoPath.

You'll find more articles by Paul Stubbs at his blog: blogs.msdn.com/pstubbs.