Demographic Tools?

I was wondering if anyone here is aware of a demographic tool or resource that does something like this.  You draw an area on a map, say like MS Mappoint, Google Earth, Google Maps or whatever, and it will give you demographic info like average household income, but more importantly tell you the number of households within that area, and the number of people. So I already have a map of my coverage area and if I could input it into such a tool and learn the population of my coverage area and the number of households.  This might be very useful in selling advertising but more important to me I could use it to convince programmers to allow me to carry their content.  This has been on my mind since I started carrying The Stuph File, when Peter Anthony Holder asked me how many households I hit. I told him about 500 which is my best educated guess but short of tediously crawling over the area in Google Earth and going cross-eyed doing it, I'd like something better. I do have one tool that does some of this

Home Town Locator  in that it gives me data for my individual smallest Census block, which coincidentally is close to the size of my coverage area (might not be for you) but it is not congruent with it.  Much of the block is west of my coverage area and it doesn't go east far enough.  Does anyone know of anything like this?
Thanks.
Jim