You would probably have to find some kind if (web) service to provide you with the distance information. A quick google search turned up this for the US, you might be able to find other services for other countries.
The new versions of Google Maps will include a java action to calculate the coordinates of addressess using the Google geocoder. These coordinates could then be used to calculate the distance.
I don't have a release date for the new version yet though, as it is still a work in progress.
This link provides a good java action to get the coordinates. The comment by Jörn gives a very nice short version to get you up and running.