Brian A. Randel just published a great article on Work Item Tracking. It can be found on MSDN VS2005 Technical Articles
The Work Item Tracking subsystem offered by Team Foundation Server exposes a rich object model for integration with your own solutions. Accessing work item information from any application only requires a few lines of code. In addition, when building an application, you can let the built-in controls do the heavy lifting to provide a rich and consistent interface. In the next column, I'll show you how to integrate work item support into the add-in that I started in the previous column.