Hi,
Yesterday I was busy to try my 2003 infopath solution on sharepoint with office 2007 all works great and go faster that is a good point (including the bug of the toolbar describing in this post
http://www.infopathdev.com/forums/topic.asp?TOPIC_ID=2311) don't appear anymore with 2007).
But one thing is very boring when you start your 2003 form on Sharepoint (sign and full-trusted) in 2007 you have always this Warning Message:

I have make a little search and found that if your website or Sharepoint Site is not a trusted site this message always appear!
So for don't have this warning message add your Sharepoint Site as trusted site in Internet Explorer(IE). For make this do the following:
Start IE-> go in tools menu-> Internet Option and in security tab click on Trusted Sites icon and after on Sites button.
Add your site and click ok two times.
You can now open your 2003 form on 2007 without warning message.
Hope this help
Thierry
Infopath 2007, Langage: C#2.0 (Modèle Objet 2003)
merci de lire ceci