Playing old demos

I know this is an old question but it's been awhile. I want to play an old demo that I think was recorded in WON. I think it was recorded just before the switch from WON to Steam, the date on the file is July 17 2003. I'd really love to see this demo again if possible.

Is there a program that can do this or am I stuck digging up my HL CD and installing the last patch (if I can find it). Help?