8  Using iproute2 you can do something like this:
echo "1 admin" >> /etc/iproute2/rt_tables echo "2 users" >> /etc/iproute2/rt_tables ip rule add from 192.168.122.40/32 dev eth0 table admin ip rule add from 192.168.123.41/32 dev eth1 table users ip route add default via 192.168.122.1 dev eth0 table admin ip route add default via 192.168.123.1 dev eth1 table users
Now you will have two routing table with two gateways.