How? Simple, download the demo for PPC and install it. Copy most of the files from your install from your Windows PC over the PPC version (except the Application, etc. - you will have to experiment as I did this like 2 years ago so I can't remember exactly which ones to exclude) and run!
You now have an OS X version of Unreal Tournament 2003! I'm not sure if this will run on the Intel side, as I just switched hard drives, and I don't have any real easy way of installing OS X there without destroying my data that I need to backup.
