first gateway box

hello all
i'm still learning the whole linux thing and at the moment i'm trying to set
up a gateway box here @home.  can someone fill me in on how to configure my
conf.d/net file?  is that the only one i have to edit?

at the moment, i have this:

iface_eth0="xx.yy.120.254 broadcast xx.yy.120.255 netmask 255.255.255.0"
iface_eth1="192.168.0.1 broadcast 192.168.0.255 netmask 255.255.255.0"
gateway="eth0/xx.yy.120.1"

that's it. outside of the commented out lines in that file, that's all i've
got.  what'd i miss?  'cause at present, i can ping my external ip
(xx.yy.120.254) and my local ip (127.0.0.1) but i still can't ping anything
in the "real" world.

i could really use your help here :)