Run it and play around with it a bit until you find out if it is the 2001/2002/3003/2004/2005 version. Also before running anything you download off that website, it might be best to do a jotti scan (http://virusscan.jotti.org/) on it just to make sure it's clean Edit: Oh, and what Norton product are you trying to install? I just assumed it was Norton AntiVirus.
Shade: In regards to your Norton Norton Antivirus is actually a mission of a program to crack. Norton has updates now that will update the software, so that if you do have a trial version and it expires... It will try to register online and their system nowadays will block already used serial keys. What you can do how ever is go to google and type in "Norton Security 2005 patched/cracked download" and find a torrent for the download. If you download one already cracked, you could possibly not have to authenticate the product online. Cant be sure though since I have a legitimate version. Give it a shot anyway and let me know how you get on.