Unable to open many apps, maybe hidden user?

I have an older Power Mac G4. Friends used it for a few months and I think they deleted a bunch of stuff before giving it back. A lot of my programs won't open (Word, Entourage, Excel....) any more. Files that say a certain app will open them won't open. I don't have any OS X disks so I can't reload. How can I find out if things are missing from applications? I need to open files and see if they are mine, what they are and be able to throw out what I don't need. I have so many items that I dont think I had before but I cant open anything. What is MF Converter.bundle, ACard 62xxM.ktext, library.vid and library.etb? I have Safari but I see in the files I also have safari:2.afploc? Can you tell me what this is and how can I open. The list goes on and on.