I would like to document within ArcGIS how the values for specific shapefile attribute fields were derived or obtained. Is it possible to input and export this information as a report with ArcGIS 10?
This is something you can add in metada - see graphic to see where you would add it within the ArcGIS GUI.
I suggest looking at the ESRI Metadata Toolkit - the XML attribute I think you want is
/metadata/eainfo/detailed/attr/attrlabl but as others have said in the comments you can use any schema you want, although Arc may not recognise it out of the box, so you will have to do some of the legwork yourself in terms of tools to work with it.