Which DVCS work best with Subversion repositories
HgSubversion provides the sort of interaction you're talking about. It bills itself as a SVN client, based in Mercurial, meaning that you work in Mercurial locally, but still interact with a SVN server.
The convert extension is also very good if you want to convert from SVN to Mercurial.
There are some other Mercurial/SVN workflows you might find interesting on the Mercurial wiki.