>>The USPS has the same kind of thing (though it wasn't on-line way back when I worked there :~)). I guess the problem might be getting your hands on one of these tables, since they're probably proprietary if not confidential...
>Not too long ago, I was doing a research project regarding market statistics by Zip and had done a search on 'zip code' through an online search engine. It resulted in numerous returns on the subject. There were some comma-delimited text files available with zip codes and lat/long data. I remember downloading some, but have deleted them. This may be one place to look at some data regarding this thread. Data is available out there that is not proprietary.

Sounds good -- Who originated this thread, anyway? We haven't heard back from that person, but the web search would be a good (and free) way to start...