Want to know about some of the deeper aspects of InfoPath integration in Office 2007? Here's a good collection: Andrew May's WebLog : InfoPath Forms in Office SharePoint Server 2007

This also includes pointers to:

• Document Information Panel: understand InfoPath's integration into Word / Excel / PowerPoint for editing the meta-data associated with the document.
• Custom Document Information Panels: you can customize the meta-data InfoPath form and you can also add your own extra XML stream to a document with an associated InfoPath template.
• Workflow forms: whew, stop your grinning and drop your linnen. How to customize the InfoPath rich / browser form associated with your work flow.

Actually, the master topic for that last bullet is here: InfoPath Forms for Workflows.