What are you talking about, custom maps and mods are pk3 files, since the gaming engine is exactly the same for mac and pc (duh) they both read pk3 files (becaused moh is based on the q3 engine) so theres not ANY difference. You can use every skinn, every mod, and every map you find on the internet, on your mac. If it doesnt work, most likely you are doing it wrong, or theres something wrong with the file...
But i guess its your fault, in that case download gameranger, its a macintosh only programm where you can chat and play games with other mac ppl, take a look in the mohaa room and anyone will help you getting your maps to work..
I play mohaa on my mac since the beginning, and I've never had any problem with maps,mods,skinns etc
In fact Im making my own mods/skinns now, ...and yes, on my mac.
and that stuff about saving money for a pc? oh please i got both a pc and a mac and believe me don't waste your money on a pc...
before i forget; here's gameranger:
http://www.gameranger.com