Craig Skibo is giving a Webcast tomorrow (April 22) at 1:00 PM (PST) on Writing Add-Ins for Visual Studio. Here's the link:
Writing Add-ins for Visual Studio
Come and learn how to customize and enhance Visual Studio to make it a tool for just you...
Craig is a member of the Visual Studio team and he was a co-author with Marc Young and me on Inside Visual Studio .NET 2003. He wrote most of the guts of the extensibility framework in VS, and so he really has an inside view of the topic.