Repairing Mac OS X Leopard without Time Machine
Reinstalling the entire Mac OS X is the guaranteed way to ensure all system components are correctly installed.

Sometimes you can get away with running a Combo Updater (the 10.5.8 in your case), it can repair a slightly damaged (or corrupted) installation.

If you are unsure of why things are missing or damaged, better to reinstall or at least run a Repair Permissions in Disk Utility. System files should be protected from deleting and you don't know if other protections are missing or changed.