I'm new here, where and how do I get this Ghostbusters Doom Game! PLEASE TELL ME!

You'll need Doom2, which can be bought or downloaded. Zdoom works better. Click on the ghostbustersdoom link on this site, and download all the files in the download, (don't miss the download in the second sentence!) unzip all your files into your doom2 folder, and it should be good to play. (You'll need winzip)