Welcome to LQ.
I'm afraid your Q makes no sense to me as it is currently phrased. In fact, it occurred to me to ask you back, "How does one do NAT with a single NIC?" Of course, I wouldn't be referring to the internals on FC4, but rather the network layout. My point is that NAT as I know it requires the source & the destination to be separate. Please explain your situation, a network diagram would be nice.
2 points about your choice of distro:[list] [*] FC4 is way out of date. [*] FC anything is for testing, RHEL or CentOS should be used for (most) servers. [list]