Looking up miles between points

Okay, I know Excel doesn't do this on it's own, but has anybody every figured a routine wherein you can plug in two sets of addresses and determine the miles between? I know I could do this easily with Google Maps or MapQuest, but we're talking about 100 different addresses. I need to find the distance between each address to use in a travel database.

If no one has every heard of doing such a thing using Excel, I'd appreciate any other advice on the easiest way to do such a thing.

Thanks,
John