A number of people have reported that the link to the companion content seems to be broken. MSPress are aware of the problem, and are fixing it. Meanwhile, here's a direct link.
Here's the main book link:
...and replying to all those people who've asked whether I'm writing an update for Office 2007, the answer is No. There are now several good books on programming against Office 2007, including these:
Programming Applications for Microsoft Office Outlook 2007, Randy Byrne
Mastering Microsoft Office 2007 Programming with VSTO, Guy Hart-Davis
VSTO for Mere Mortals: A VBA Developer's Guide to Microsoft Office Development Using Visual Studio 2005 Tools for Office, Kathleen McGrath and Paul Stubbs
Microsoft SharePoint: Building Office 2007 Solutions in VB 2005, Scott Hillier