Microsoft Learning and Roger Jennings have a new book out through Microsoft Press - Introducing Microsoft® Office InfoPath™ 2003. This book covers InfoPath from top to bottom including the SP-1 feature enhancements and developing InfoPath solutions using managed code.
From the book's description:
"Learn how to integrate forms with other Microsoft products such as Microsoft SQL Server and Access databases, Windows SharePoint Services, and XML Web services. This book also provides an overview of the technologies used to build an InfoPath forms solution using Visual Basic .NET managed code and the InfoPath Document Object Model (DOM)."
You can find a little more information, including how to order, at http://www.microsoft.com/mspress/books/6511.asp.