It is a difficult problem at best. DNS will resolve names to numbers, but only associates a single name with the reverse lookup. There is nothing stopping anyone from pointing their domain to your IP address, it just doesn't do them much good.
If you had a subset of names that you expected to be associated with a specific IP address(es) you could query them all (I wrote a PERL script to do this once). Not quite what you are looking for though, I think.
pansophic