I hope, BDAqua's suggestion will work to repair any permission problems. Which version of iPhoto is installed on that Mac? On my old G4 is a newer system installed, and probably a newer version of iPhoto. My memory of this old version is rather vague, and unfortunately I just trashed my version of the old "Missing Manual" for iPhoto.
Have you looked in the Pictures folder , if there is an iPhoto Library? For the first iPhoto versions the photo library has been just a set of folders and not a closed package. If there is an iPhoto Library folder, check the inner folders. Are there folders named "Originals" or "Edited" or "Masters"? If yes, copy the folder to an external drive.
New versions of iPhoto have a built-in First Aid tool. I am not sure , if the First Aid dialog has already been introduced in iPhoto on Tiger.
You could just try it, if you can launch iPhoto in the Repair mode. But first make a backup of the iPhoto Library.
To repair follow the directions here: iPhoto 6 and later: Rebuilding the iPhoto library - Apple Support
Perhaps Old Toad or Terence Devlin can remember the old iPhoto versions better than I do.