[llamabeast]

I believe the mac terminal is very similar to the linux terminal (being also based on unix). So here's how I do it:

First go to the dominions directory. For me that's:
cd ~/dominions3

For you maybe something like:
cd ~/Applications/dominions3
or something, I have no idea really. Anyway, it sounds like you've already found it.

Then, once in the Dominions directory, type:
./dom3 -dd

That should work I think. It does for me.