Best bet is to reinstall the system. This will also rid the computer of any software that you do not wish to include as part of the sale and give the new user a nice clean start.
Before blowing the system, I would do a secure erase of any personal files especially banking or accounting items.
Just do a basic OS install. Be sure to give the new owner the original install disks and original iLife disks. If the computer shipped with Panther and you are selling it with Tiger you should also include the Tiger install disk.
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