A quick browse did not reveil any licensing information for the data. Maybe it’s best to specifically ask if their data is compatible with the CC-by-SA 2.0 license which we have now.

If the license is no problem then you might want to use the shapefiles because there is a shp2osm converter available somewhere in the osm svn repository.

Edit: Oh and maybe you want to talk to OSM user Dave Hansen, who has imported the tiger data into osm. He will certainly be able to give you advice on how to proceed with the import.