Firewall and Proxy Server HOWTO

I am attempting to follow the 'Firewall and Proxy Server HOWTO' written by Mark Grennan, but have been running into a problem in section 6.4. When pinging the outside address of the firewall from a computer on the LAN, it works. At this point of the test process, it shouldn't. IP Forwarding is turned off, and I have turned off IP Masquerading. Can anyone provide me with some guidance? Cheers, Art Sloate