I'll provide outline information here. Someone else can make this pretty for people who aren't comfortable with unix.
First, you want to create a subinterface. For physical ethernet interfaces this is real easy in OSX, as you can just "duplicate" the interface in System Preferences, but for some reason it doesn't allow you to duplicate your wireless card.
Whatever. Open a terminal and sudo to root. ifconfig is a command that shows you your network interfaces.
ifconfig -a
will show you all of the network interfaces on your machine. On my ibook my wireless card shows up as en1, so I can create a subinterface, or alias, by typing:
ifconfig en1 alias 192.168.1.1 255.255.255.0
If you do this, make sure that: 1. Appletalk is turned off. 2. You are using a different IP address range then the one currently configured on the interface.
Once you've done this, you can tell your computer to route by typing this:
sysctl -w net.inet.ip.forwarding=1
If you want this stuff to survive a reboot, you'll have to create a startup script for it. There is some information about that here:
http://www.afp548.com/Articles/Jaguar/startupitems.htmlIf you need to do NAT then you should look at these articles:
http://www.afp548.com/Articles/system/natserver.htmlhttp://www.afp548.com/Articles/Jaguar/nat-ipfw.htmlSome of this stuff is OSX server specific, like serving DHCP. There IS a way to serve DHCP on any OSX machine, probably involving a fink package, but I don't have time to research it right now.
If you are not serving DHCP, the obviously your friends who are connecting through you will have to configure their network interfaces with IPs in the range you've setup and with you as their default gateway.
I haven't fully tested this. Its a little odd that the control panel doesn't let you dupe the wireless card, but I can't think of a good reason why this wouldn't work. You can certainly create aliases on the command line.
Hope this is useful...
