: ok i went to the link one of yall gave me and it does not work.do i have to
: get some kinda computer program on my computer to play?
first of all you download the Marathon data files, go to http://source.bungie.org/get/ and there you will find everything you need. It's probably the wisest choice to start by just downloading Marathon 1 scenario and ignore Durandal & Infinity (which are Marathon 2 & 3).
After that you need the game engine to run those data files. In the row below the scenarios is the game engine for the various operating systems available. OS X, Linux & Windows. Download the proper OS version of the engine.
Now you should have all the essential files. Now the only thing you need to do is to drop the game engine (Aleph One) to the core folder of the Marathon scenario and then double click the Aleph One icon.