Rick Ayers from ESRI sent me the attached note (inst.doc) that explains how to download redistricting data at the geographic detail of County - census blocks from the ESRI website at:  For those who want to convert Census data into ESRI shapefiles, I think the method Rick describes is easier to use than the one I wrote down to this listserve a while ago.
Claritas Inc. is also making Census data available for free downloads from their website at:
Thank you
Nanda Srinivasan