If I reinstall OS X 10.4.11 . . . Will I loose the installed software and files???

My PowerBook G4 has slow performance. Does anybody know any free software to make a "DEFRAG"???..... I want to reinstall its OS X 10.4.11 but I have a lot of information so, I do not want to loose the information: installed software, documents, presentations, music, videos, pictures, etc.

And here the main question: may I reinstall the OS without loosing inofrmation and installed programs???

Third. If I reinstall, I suppose that all the installed software will be lost. Is fine to me because my major concern is the information.

Thanks in advance.