Your computer name should be displayed, if you have file sharing turned on. I think it also displays via the Bonjour features of OS X. If you haven't changed it from the time you set it up, the system uses name data you entered at setup. You can change your computer's name by opening System Preferences > Sharing, then entering a new Computer Name.
I also changed my short name to something generic, e.g., "Main", because the short name gets embedded in a PDF file when creating the PDF -- at least using OS X's feature. In Leopard (I can't recall for older versions) you have the option of changing it at the dialog box.