I also posted this as a “comment” on Cathy’s post, but suddenly wasn’t sure if I needed to be logged in to post it that way (which I wasn’t). So, sorry for the repetition, but this is a response to Cathy’s post:
Cathy, I have seen some exciting things done with Google Maps/Earth API to create the kind of thing you are talking about (not that I know, really, how to do it), but we might look at some of the possibilities together: code.google.com/apis/earth/documentation/examples.html
Also, did you see this site dealing with visual depictions of what was there in the past? posterityproject.blogspot.com/2011/04/whatwasthere-maps-your-journey-to-past.html