Found this but the link is dead:
So what folder/file to I replace with that code?
We created a fix for the game not starting up on Windows XP 64 and Windows Server 2003 systems. This patch has not undergone the same amount of QA as the released demo so I strongly encourage to ONLY replace the UT3Demo.exe with the one from the patch if you are experiencing the "Modified executable code is not allowed" issue at startup.
http://www.epicgames.com/download/UT3Demo-XP64-2K3.zip
UT3Demo.exe md5sum: 9ac494f243bdd6d71c2d612d8d98fba3
So what folder/file to I replace with that code?