problem:
3 nic's
Main nic(eth2) shares internet and at once only one(eth0) nic talks to it from two. Another one(eth1) no mather what is unreachable. Noticecd that, firstly ifuped nic, gets atention from main nic - but not both. 

situation: 
home - 3 pc's 
and 3ethernet cards  
and 2x crossover cables...

point:
share internet from pc0 to pc1, pc2
(from eth2 to eth1 and eth0)
set pc's in to lan all acesible each to other

ethernet cards are working - no errors, checked separately each
ip forwarding is on, i think its enough (!?):
/sbin/iptables -t nat -A POSTROUTING -o eth2 -s 172.16.1.2 -j MASQUERADE
/sbin/iptables -t nat -A POSTROUTING -o eth2 -s 172.16.0.2 -j MASQUERADE

heh..?

# home pc0 with whole world... 
auto eth2 
iface eth2 inet dhcp

# to home pc1 (172.16.1.2 gw-.1.1)
auto eth1 
iface eth1 inet static
address 172.16.1.1
netmask 255.255.0.0

# to home pc2 (172.16.0.2 gw-.0.1)
auto eth0
iface eth0 inet static
address 172.16.0.1
netmask 255.255.0.0