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Look for the Microsoft Help document, Distribute the contents of a cell into adjacent column.
Preserving Leading Zeros and Keeping them Formatted as Text
Most STFID or GEOID numbers are stored as Text in the Tiger Line Shapefiles you use to visualize the boundaries of states, counties, and cenusus tracts. In the files you download from the Census Bureau, these numbers are automatically converted into numbers by Excel. This means that, when you try to join your data to the shapefile for analysis, you won't be able to properly join according to the geographic identifier attribute. There is a quick solution to this located here:
http://www.facebook.com/topic.php?uid=98595894086&topic=17703
Once you follow the steps to get the leading zeros to remain, you must then create a new column and format it as text. Then copy the data from the calculated field (=TEXT (A2, "00000") and use the "paste special" command to paste the values into the new, text-formatted column you created.