Mike from SoCalGIS.org just posted an excellent tutorial showing how one could use Python within the field calculator to break apart string values and add them to a new field.
For example, say you have a field with values such as “Census Tract 12345″ and you want to have a field that only contains the tract number (e.g., 12345). You can use python within the field calculator to extract that third word from the field, pretty sweet!
Check it out:
http://socalgis.org/2013/12/05/field-calculator-i-just-want-the-third-word/