LinuxQuestions.org - A couple of IP masquerading questions

Ok, I have a bit of a strange situation here. Recently I was asked to segment off part of our internal network by using a Linux box. This system is running Fedora 1 and is already acting as a fileserver. The existing internal network is already set up on 192.168.8.0/24, and I'm trying to set up the new segment as 192.168.108.0/24. So, I have 2 NICs installed and configured, and I followed the HOWTO guide here. Things were set up without any problems, and systems connected on the new segment can ping systems on the old one, but can't access the internet now. The box doing the masquerading also can't access the internet anymore either. So, I'm a bit stuck, trying to find out why things partially work, but not entirely. So, a couple quick setup issues that were not covered in the HOWTO:

1. I know the gateway address of the systems on the segment are supposed to be setup to the one doing the masquerading. What gateway should I be using on the internal NIC on the masquerading box? It's own IP?

2. It appears now that if I disable the secondary NIC, I lose all outside connectivity, as if it's only trying to use the second card for access. So, while the second card (used for the new segment) is active, I can attempt to ping outside IP addresses and just get a "Destination Host Unreachable". But, if I disable the secondary card, I will get a "connect: Network is unreachable". It's not even trying to use the primary card that's been working all along. Internal network access still works fine though. :confused:

Any suggestions would really be appreciated here.

Thanks in advance.