Does anyone have suggestions on software or a database that can be used to calculate the driving distance between two zipcodes. We have used ZipFind but that just uses the lattitude/longitude to calculate distance. We need to calculate driving distances. MS Mappoint does it but it's way to slow. The US Postal service doesn't seem to sell information that contains distances, they just have lattitude/longitude of the center of the zipcode. Any suggestions?

Jeremiah Johnson