Google Maps probably has a function you can use, via the Insert from URL script step (probably using httppost to access the web service). However, I hear that the services is limited (you can't access it too often.)
Then, you need to find a custom function, or just an article on calculating "great circle" distances.
Finally, whatever service you use to get the address, this might help you parse the results:
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To get an address from just any pair of coordinates, you need to do what's called reverse geocoding. Here's a blog post describing how to do that.
It isn't clear from your question whether you're just looking for whatever address is at a coordinate pair, or if you want to link a coordinate pair to an address record you already have. If you want to do the latter, you need to geocode all your addresses first, and then you can use the techniques in this blog post to associate addresses you get in the field to addresses in your database.