<p>I'm the creator (and so far, only developer) of a CodePlex project.  I've writing it on my laptop, using a Subversion repository on my home network.  </p>

<p>Submitting my changes to CodePlex via the TeamServer interface is driving me crazy, and I'd really like a simple way of syncing my svn repos with CodePlex via there new SVN interface.  svnsync or synmerge seem to be the way to go, but neither's instructions seem clear to a guy who's only ever used TortoiseSVN. And they seem to also seem need local access to the destination server (which clearly for CodePlex, is impossible)</p>

<p>So, could someone give simple instructions how to do this?</p>

As you'll find in the
documentation
, svnsync requires exclusive (but not local) access to the destination server. This makes it unfit for your purpose, as it would render the CodePlex repository inaccessible for commits by other developers (when they come ;)).
You might consider the other way around though: always commit to the CodePlex repo, and use svnsync to keep a local (and read-only) mirror of that.