OS 10.2 - Permanently deleting emails and files

This is my first time posting so I hope I don't screw this up...Does anyone have any advice on how to permanently delete emails and files? I am running on OS X 10.3.9 and have deleted files in my trash using the secure empty trash function, however, I have a large number of emails I have deleted in Mail. Are these permenently deleted as well? Secondly, is some of the shareware or freeware out there such as Shredit any good? I have a concern that someone is going to try and retrieve deleted data off my computer sometime soon and I really don't want any emails/files showing up that I have deleted.

If you are using Mail as your email client and you account is setup as a pop3 account not leaving a copy on the server and your mac is not remotely backed up and your home folder is local then your mail lives in /Users/username/Library/Mail. Using the erase deleted messages from the mailbox menu will get rid of your mail. Will it be recoveerable from a drive recovery company,...possibly. Your company on the other handprobably not. Unless the above criteria is false.