Try connecting to it as WMs connection.
Simply add a new WMS layer in Display Manager:
Data > Connect to Data > Add WMS Connection
- Add http://wms.latlon.org/?layers=osm and version as 1.1.1
- Cick Connect
- Click Login
- Check OpenStreetMap mapnik
- Click Add to Map
Supportting the troops daily.
If you were to consider third party add-ons, MapWorks Base will import .OSM files directly into Civil3D (or plain AutoCAD). The files are in lat/long and are projected to a designed plane system assigned to the current drawing.