Replying to Question About Leopard

Okay so i have a macbook that is about a year and a half old.  I'm running Tiger on it.  After this much time i obviously have a lot of files and things built up and things that i do not want to lose. 

I have gotten my hands on a copy of leopard.  It is a legit copy that has never been used.  My question is what will happen to all my files/programs/preferences if i install leopard?  Will i lose everything or will it organize itself in the new OS.

Any help is appreciated. +K

I also searched on the apple site and found nothing.