A: This is a thorny question. The President of Westlake, Phil Sulak, has been quoted by Macteens as saying that:

While we don't have any plans to release Mac-based tools, the Mac version of Halo should be fully compatible with the Mods released by the PC Halo community.

However, shortly thereafter, Peter Tamte of Destineer Studios / MacSoft, who are publishing Mac Halo, said the following:

[...] we've made the decision never to talk publicly about editing tools until they're pretty much done. Sorry I can't offer better info than this. But, it's the honest truth. Do we want to make editing tools for Halo available on the Mac? Of course we do. Am I going to imply or promise that they'll be available? Not until they're pretty much done.

Sulak did go on to say that:

My guess is that if Mac Halo does extremely well at retail, MacSoft will consider having us port the editing tools over.

So, when all is said and done, is anybody working on porting the Halo tools right now? Unknown. The President of the company who'd be doing that work has said they have no intention of doing so, which would seem to indicate "no". The publisher seems to indicate that perhaps that work is being done, or might be done-- whether by Westlake or some other party is unclear.