AFAIK, the XP cap remover is _not_ an exe mod, so it should work fine on a mac. Vaskez - The local resident expert on modding - posted a while back on how to make your own, but that does involve editing a file, and the utils for that might not run on a mac. Just download a regular remover and try it. The best one is apparently on Baldurdash.
http://members.rogers.com/mrkevvy
This link was funtional earilier today.