There is no way to get coordinate positions of your target or anyone else. The only way is for other players that are using addons to send that data to one another from their respective GetPlayerMapPosition calls.
You can only guess at ranges based on whether certain spells/abilities are in range.
Here's an example:
http://www.wowinterface.com/download...82-Fudge2.html
Another example would be the range displays in Stuf unit frames. (0-5yards, 5-10, etc)