The map can be viewed here: http://www.gravitystorm.co.uk/osm/
(check it out, it looks fantastic; highlights include relief colouring, contour lines and specially produced map icons)
Andy blogs about it here: http://www.gravitystorm.co.uk/shine/archives/category/openstreetmap/
To add the map service to TangoGPS create a new repository with the URI:
No screenshot I'm afraid, because I'm trying out today's OM2008.8 release and the screen-cap application is refusing to install. It does look awesome, however.