As with Vista, the Office 2007 system presents a fantastic new opportunity for software developers and ISVs. To make sure you are taking advantage of this check out the Office dev center over at MSDN which has lots of info on how you can code for the new platform.
Some of my favourites are:
Alternatively check out all the resources here:
Access, Excel, InfoPath, OneNote, Outlook, PowerPoint, Project, Visio, Word
Project Server, SharePoint Server
Tools and Technologies
Add-ins, .NET in Office, Ribbon, Visual Studio Tools for Office, Windows SharePoint Services, XML in Office