Ling Bao, one of our Team Foundation PMs just sent this around:

The VSTS Beta 2 Extensibility Kit is now available for public download at http://www.vsipdev.com/downloads/ or via the link below.  It contains refreshed content and samples for the Beta 2.  This info will eventually be organized into the VSTS portion of the Visual Studio 2005 SDK: 

New Visual Studio 2005 Team Suite Extensibility Kit for Beta 2
The Extensibility Kit for Beta 2 provides an early look at the extensibility points and is the basis for what will become the Team System SDK. It’s provided “as is” and without formal product support. It is intended to give an early look at how customers and partners could extend Team System functionality.   

This is a really important download for anyone wanting to understand how to extend Team Foundation. Amongst other things for Work Item Tracking there are samples in VB & C# showing how to code against the Team Foundation Work Item object model (for example to programatically create work items, add attachments, link two work items together etc) plus command line tools to enable importing/exporting Work Item Type definitions to/from an existing Team Project (something I've talked about a little bit on the forums, and I'll blog about in more depth in future).

It also has a number of presentations, and a huge amount of material on extending all the other Team Foundation Components (source code control, process guidance, reporting, test tools etc)

It's a 47MB download, so it's not small - but in comparison to the rest of VSTS it's not too massive either - so come on folks, let's see what great new tools you can come up with!