We would usually do that by separating the data entry box, and the field containing the accumulated data.
Create a global field 'DataCapture'.
Create a script for a button beside that field that when clicked sets the DataField to be something like:
"------- Added by: " & Get (AccountName ) & " at " & Get ( Current TimeStamp) & " ----------------¶" & DataCapture & "¶¶" & DataField
Make the DataField not modifiable in browse mode.
It makes more sense to me to not put all of this data in one field.
Each entry, IMO, would be a separate related record with a field for the account name, a field for the timestamp and a field for the text to be added.
A portal can display all of the data in each record and a lock expression in Manage | Security or a validation calculation in Field Options can keep users from editing a new entry once it has been comitted.
THanks for the replies. After looking at what we were trying to do we will seperate the data to individual entries and create a report to view it all.