You don't. For certain columns (ones which are not used in any schedule
calculations) you could have a macro which encrypts the data but that is
only a work-around. Some people export the data to excel and then delete it
from project and re-import it when needed. Make sure you include task unique
ID in your export so you can re-import and merge correctly.
--
-Jack ... For project information and macro examples visit
http://masamiki.com/project
..
"Help with vba in Project 2003"