These are the 2000 Redistricting Census TIGER files for Montana, in their native TIGER/Line format.  They were avaialable through the NRIS web site in the 2000s.  See the tiger2000.TXT file for FGDC metadata from the Census Bureau describing the files.

The TIGER/Line format is an acsii format for which a full technical description might be hard to obtain and which is probably not supported by modern GIS software.  The data, converted to shapefile format, is available on the GeoInfo web site.
