I have created a custom object which is going to be used for an internal support team.

Users will be entering in comments into the 'Comments' field that need to be date/time stamped and retained (nobody except sysadmin can edit once saved).

Only solution I can think of (but do not know how to accomplish):

There is a long text area field that comments will be entered.  When the record is saved, I would like to cut the text in this field and append it into another long text area field with a date/time stamp at the beginning of the line.  I can then make this field read-only to everybody but the sysadmin profile.

Help would be greatly appreciated!