Ok, here's an update: pfSense is working fine on a different box (the one the store owner wanted to sell me in the first place!). The errors went away on that box when the 2nd NIC was installed and it boots without error on that machine. The firewall is configured and running smoothly now! :)
The Netvista box wouldn't run with anything. I'll play with that when I have time, but it's not a priority.
And pfSense still doesn't boot on my Acer Aspire 5520-5912 AMD Turion X2 laptop, "oopsing" and spilling registers while still in the boot loader. I'm taking a wild guess it doesn't like 64 bit chips or laptop hardware, but I really have no idea since it doesn't even hit the kernel yet when this happens.
Thanks again to everyone for the help. And as far as the thread on adding stuff, I'll make sure to read that later–maybe it is better, even on such a simple network as this, to run one machine as dedicated.
Mike