This Preview includes bug fixes and performance improvements to InfoPath 2003, in addition to a number of feature enhancements directly resulting from customer and partner feedback. The Preview is 100% compatible with existing InfoPath 2003 solutions. When developing new solutions with the Preview, you will have a choice to create forms fully compatible with InfoPath 2003 or forms that take advantage of the new feature enhancements, which include:
More control choices, including Master/Detail, File Attachment, Recursive Section, and Choice, as well as custom-authored controls..
Better schema support, including built-in support for schema changes.
Printing improvements, including page breaks, margins and print settings.
Improved e-mail deployment of sandboxed solutions and auto-updating of trusted solutions.
Better management and categorization of solutions.
Tablet PC support improvements.
Increased support for rules and roles for declarative business logic.
Enhanced XPath expression support, including calculations without writing script.
Additional data adaptors for email and SharePoint Products and Technologies lists.
Better support for custom migration plug-ins.
Enhanced Object Model (OM), including OnSave event, offline state, submit, and digital signatures.
Improved support for secondary data sources.
Additional support for business logic written in managed code (requires a separate download).
Enhanced OM for external automation and windowless mode for application-level calls.
Better support for ADO datasets and diffgrams to round-trip data changes.
Additional support for complex scripts, such as right-to-left and South Asian languages.
Enhanced support for digital signatures, including partial signatures, non-repudiation, co-signing, and counter-signing.
Improved stability and performance, including auto-save and data recovery.
There's more detail on the PressPass page. There's also a VS Toolkit for InfoPath available. And remember this is a preview release, so usual cautions apply! Woo Hoo and Happy Monday!