oh it looks like its available on MSDN
"InfoPath 2003 Toolkit for Visual Studio Tools for Office 2005
(English) "
Description ........
The InfoPath 2003 Toolkit for Visual Studio .NET 2003 has been updated
for Visual Studio 2005. It will automatically upgrade Visual Studio
..NET 2003 projects so you can leverage your existing work.
Support for InfoPath means you can add business logic to your form
using managed code instead of script. Managed code allows you to use
the Microsoft .NET Framework common language runtime (CLR) to write
code in Microsoft Visual C# or Microsoft Visual Basic, and to make
calls into the .NET Framework class library for advanced tasks such as
digital signature processing and encryption/decryption
