Enter the word "private" in the search box above and study the results; you will find some suggestions on how you could create a private database or a private overlay (e.g. http://help.openstreetmap.org/questions/6329/create-private-overlays). Depending on how you want to present your own data, a KML file displayed on top of OSM using OpenLayers might be a good idea; if you want to privately modify OSM data then you will have to set up your own rendering (plenty of answers to that on this site as well).
answered 27 Feb '12, 08:07
Frederik Ramm ♦