I was poking around the MSDN subscribers download site today (in between checking out Hotman Paris Hutapea's Liberace style bling bling) and found this:

It's the InfoPath 2003 Toolkit for VS 2005, which is great for those who want to start playing around with InfoPath .NET development with VS 2005, or if you want to start migrating your existing InfoPath 2003 .NET projects across. Either way, download it, install it, develop against it, love it! Or Granny Gonna Get You!