Spent all day fighting this, but I now have polygons working. To experience it for yourself, click through to the map, click on Peloponnese - BAM! Polygon.
While doing that I also ripped off an OpenLayers applet for creating polygons:
Now we can begin to create regional outlines for other areas, like Boeotia and Arcadia and so forth. There's a handy Wikipedia article on this precise topic here: