The easier way si to have a router with wired ports and to plug both PS3 and your MAC in it. This would automatically set yor PS3 and MAC (using DHCP) so they can see each other.
The same goes in majority of cases if both (or one) of the devices is connected via WiFi to the same router.
If you're though planning connect directly PS3 to your MAC (or PC) then you'd need to set up the addresses manually. Dont worry about DNS, just set up both devices in the same range, for exacmple like this:
Default gateway: 192.168.0.101
MAC or PC
Default gateway: 192.168.0.100
As you might have noticed the "trick" is to keep both units visible to each other by having first 3 bytes of IP address the same and by having DIFFERENT last byte - can't be the same - and by "pointing" to each other the way the IP address of one unit is Gateway for the other one and vice versa.
Hope this helps.