Instead of going for the [manual copy solution][1], you can opt to go for the [StreamingAssets][2] route. 

Create a folder within your Unity project named "StreamingAssets" and place your XML files in there. Upon build, Unity will then create a verbatim copy of this directory. Your XML files will be accessible at `string path = Application.dataPath + "/StreamingAssets";`


  [1]: http://gamedev.stackexchange.com/a/44592/11127
  [2]: http://docs.unity3d.com/Documentation/Manual/StreamingAssets.html