According to the OSM [wiki][1] it is generally possible to use OSM based maps on the Germin Garmin Nüvi 1490T.
So with this entry point [OSM_Map_On_Garmin][2] you should be able to download a map for your area, copy it to your garmin device and enjoy.
When there are problems or errors in detail, you can slao also aks at the [OSM forum][3] at the Garmin subforum.
[1]: http://wiki.openstreetmap.org/wiki/Garmin/N%C3%BCvi_series
[2]: http://wiki.openstreetmap.org/wiki/OSM_Map_On_Garmin
[3]: http://forum.openstreetmap.org