Message Security and Delegates

Using exchange 5.5 on an NT 4 domain…

If a user applies private permissions on a message, calendar, appt, etc. will a delegate of that user be able to open/view/modify the information? If so, what security measures can be taken to prevent suchaccess? If this is not possible via exchange 5.5 (ie. administrator access rights to mailboxes cannot be changed easily), does exchange 2000 have this type of security built in?