What do your IP/Gateways look like for the various network cards? Do they overlap? And do you really need the devices seperated with your computer in the middle?

Assuming you're using 192.168.x.x for your internet connection, I'd go ahead and use 10.x.x.x for your "devices attached to the computer". Make sure you don't have a gateway specified at all for your 10.x.x.x network configuration.

Matthew