Hi Anson,
as far as I know, if you are designing an Office InfoPath 2007 form template for a browser scenario, it should be noted that filtering is not supported. Filtering browser-based forms is only supported with InfoPath 2010.
If you want to filter a browser-based form with InfoPath 2007 there´s a workaround which is published by the InfoPath team.
Please have a look at the following link for further information:
http://blogs.3sharp.com/davidg/archive/2007/01/16/2787.aspx
Regards,