Edamno has released a VB.NET library for creating various shell extensions
- Browser Helper Objects
- Context Menu Handlers
- IE Menu Buttons
- InfoTips
- Property Sheets
- Thumbnails
http://www.mvps.org/emorcillo/dotnet/shell/shellextensions.shtml
He also has a library for working with Windows Task Scheduler, and, most importantly, a library for working with OLE Structured Storage. Now you can read and write the author and comments associated with a file!