It is my understanding that with IP2010 you can use filtering on a browser form.
Also, you can use IP2010 to create a IP2007 form for MOSS 2007.
However, even if you use the IP2010 product to create a IP2007 form, filtering on a browser form is still not available.
Is this a correct assumtion? ( I have not tried any development in IP2010 yet).
I would love to be able to filter a data source used for a drop down list in a browser form.