ArcGIS online

ArcGIS Online includes ArcGIS Explorer (requires Silverlight), a free online browser for ArcGIS datasets.  OpenStreetMap is an available basemap through this interface. 

ArcGIS OSM importer

ArcGIS can import bz2 compressed .osm files to a file geodatabase using a python script called "OSM Loader" (Version 2.0 by Dominic Stubbins) that doesn't use an XML parser!  The script can be downloaded from www.arcgis.com