>>This looks like it might work for you:
>>
>>http://www.a1vbcode.com/snippet-3557.asp
>>
>>(You will need a database with the longitudes and latitudes)
>
>Thanks, I thought there was a formula to calculate from the postal codes directly without having the need to get the latitude and longitude. I'll see more about those options.


There's also this http://geocoder.ibegin.com/downloads.php

US zip codes with longitudes and latitudes