Yes, for a custom config like this you may be better removing network-manager.
sudo apt-get remove network-manager
Edit the interfaces file to have two sections one for each network card. You don't want 0.0.0.0 as the gateway, you want the actual IP address of your router connected to the internet.
Here's an example but you will need your own values,
(this is my router interfaces file)
Use iface ethX inet dhcp when you want it to get it's IP from the DHCP server, and use iface ethX inet static when you manually set it's IP value. For your internet facing network you likely want dhcp but for your test interface you may not if there is no DHCP server on that network segment. You only want a gateway statement if there is a router on that segment that can get out to another network. ie. single network = no gateway, multi-network (like internet) = need gateway. Your router is your gateway.
# The loopback network interface
iface lo inet loopback
# The WAN network interface
iface eth0 inet dhcp
# The LAN network interface
iface eth1 inet static
inet is just the address family, for normal stuff that's what you want. See man interfaces for more details. You can do so much more here as well but this is the basics that should get you started.
After editing interfaces you must restart with,
sudo /etc/init.d/networking restart