Heya,
I was looking around at Doom source ports, seeing if any worked on Macs, and ended up getting the latest version of Odamex (0.4.2) working on OS X 10.5. I didn't see any up-to-date version for Mac OS; a version of 0.4.1 was linked to in a forum post, but not 0.4.2. I ended up using XCode to build a copy of the main executables (odamex, odasrv, and odamaster), as well as the mac launcher. The result seems to work ok, and is able to connect to existing servers.
Is a build of 0.4.2 available? If not, I'd be happy to upload a copy somewhere.