OK so I took the html delivered by openstreetmap.org for an embeddable iframe (as referred to by the exported embedded html from The Map), modified two lines: change the script line referring to openstreetmap version of openlayers.js, to refer to the development trunk (http://openlayers.org/dev/openlayers.js), and added a new Graticule control to the map, and voila! a basic mapnik map with grid overlay and coordinates displayed.
Html looks like this:
OpenStreetMap Embedded html { width: 100%; height: 100%; } body { width: 100%; height: 100%; margin: 0px; } #map { width: 100%; height: 100%; } .olControlAttribution { bottom: 3px!important; }