OK, so for using a serial link issue the following command from the Mac OS X Terminal:
sudo /usr/sbin/pppd /dev/tty.KeySerial1 38400 noauth local passive proxyarp asyncmap 0 silent persist 192.168.100.43:192.168.100.44
That should be one whole line. sudo is necessary, because launching pppd requires root privileges. /dev/tty.KeySerial1 is my serial port (which in my case is a KeySpan high speed USB-RS232 adapter, BTW) This will probably be different in your case if you use a different make or model. 38400 is where you'll put the desired bitrate. Start with something low and safe like 9600 initially and when you get it going, work your way up. Now for all the rest of the parameters I will have to refer you to the manpages of pppd, because that would be too much to get into here, although above parameters are good defaults to start with (unless you desire authenticated PPP, which is kind of overkill for a nullmodem connection). The last parameter is 2 IP addresses. The first one is the IP address of the PPP device on your Mac and the second one is the one you'll use for your Amiga. Please replace these with values you use for your own internal network.
If you get it working you can add pppd to your startup file /etc/rc, so the ppp daemon will always be waiting whenever your Amiga wants to connect. Once again you'll need root privileges to edit /etc/rc, so do:
sudo vi /etc/rc
I simply added the pppd line to the end of the /etc/rc file. Ofcourse you can drop the sudo part here, because the /etc/rc file is already being executed with root privileges.
If you need any help configuring your TCP/IP stack and/or PPP software, just shout. I can post my relevant AmiTCP configuration files and my AmiPPP config here if you want, but that'll probably be tomorrow evening at the earliest. For now good luck!
