Your question isn't clear and more information is needed. What, specifically, is the problem? (What are you trying to do that sometimes is successful and sometimes is not?)
Is there any routing in your (the) network? Or is the topology flat so that the source and destination traffic is all on the same switch?
To answer your questions:
1. Yes, IOS 12.1 supports the "Macintosh" or AppleTalk protocol. But out of curiosity, since OS X supports native IP, why not use that?
2. Technically, you could stress a 2924 hard enough to cause it to have peformance problems. What are you trying to do across the switch? But there isn't a direct correlation, per se, between the number of ports in use on a switch and performance degradation.