I don't think you can do it directly in lisp, you can however use a few API calls to return it, but as I am not always ready to accept defeat just because someone says it can't be done.....
You could look at importing the API import function into VLisp, then perhaps using that to import API calls into the VLisp environment, once you do that you can call the wsock32.dll directly using the API call and retrieve the IP address there...it is a long shot, possibly lots of coding, merging VBA, C++, VLisp and lisp into a single program....sounds complicated...