I have received this question multiple times in my InfoPath sessions. Can we have one dropdown being a filter for another dropdown in an InfoPath form. I always do a demo showing off the power of the rules in InfoPath with a selection in a dropdown updating fields in textboxes on the form. That is pretty easy. A cascading dropdown involves some work as I tell people all the time. I have not found a time to really come up with my own solution but I have been researching other InfoPath stuff today (document conversions and why I can't convert to png on a beta 2 TR machine) and I came up with a very recent post on the InfoPath team blog detailing the steps what you have to do to come up with cascading dropdowns. Thanks guys...it saves me some work and now I can point people to your posting!