I have downloaded some of SEDAC's 1980 census tract boundary files in "BNA" format, but am unable to read them in Arc GIS 8.1. I was told that there should be a conversion program "bna2shp.exe" somewhere on your site but am unable to find it.
There is a script from ESRI’s ArcScripts site that converts Atlas bna files to shape files, please see: http://arcscripts.esri.com/details.asp?dbid=11491