This is how http://informationfreeway.org/ does it. Look at the source for more info.

    layerTilesAtHome = new OpenLayers.Layer.TMS( 
        "tiles@home (direct)", 
        ["http://a.tah.openstreetmap.org/Tiles/tile/", "http://b.tah.openstreetmap.org/Tiles/tile/", "http://c.tah.openstreetmap.org/Tiles/tile/"],
        {type:'png', getURL: get_osm_url, displayOutsideMaxExtent: true }, {'buffer':1} );

        map.addLayers([layerTilesAtHome]);

If you use the “generatetiles.py” script, then the contents of the “tile dire” is what you get b going to “b.tah.openstreetmap.org/Tiles/tile/