Well I did go ahead and put in the third network card in, and then had to reboot a few times. The one I added uses the same module as one of the other cards I use. And there is no monitor on the machine, so it was a fun time finding out where each cable had to go. My existing network is 192.168.0.x, I am going to set that card as 192.168.1.1. Now to figure out how to get my DHCP server to talk to that address as well, but not the internet one. (I've preferred to bind services to only one card instead of having massive firewall rules.)