#3 Forwarding traffic?

[Anonymous]

I guess this is a very basic question, but I haven't been
able to find the answer in the documentation:

Exactly how do I set up services like ftp or ident to be
forwarded to a PC on my LAN?

I have tried setting up a NAT from Internet (eth0) to my
PC on the LAN (eth1) choosing the appropriate service,
but it doesn't seem to do the trick. Do I have to set up a
rule from Internet (or FIREWALL?) to my PC too?