As seen on The-Ctrl-Alt-Del.com: I have talked to a couple people on EfNet who continue to rave about how great the demo (beta?) is. Personally, the zip I got crashed my system not even 5 seconds into the game. However, the installer and file dates all seemed to be legit. The zip's filesize was around 150MB. I don't think there is more than one version of the demo floating around, so it looks like some people are having luck with the one that was found. The demo was apparently also not designed for the public, it was supposed to be a corporate version. (?? meaning, for beta testers? Internal? I'm not sure...
Download Unreal Tournament 2003 Demo Leaked