router with multiple routes

hi all. i have to setup a linux box to act as a router. it will do the
work of a cisco router/fw.


lan 192.168.0.0/24
********|
********cisco router/fw* ( then the linux box )
****192.168.0.253*(eth0*)**->
****->*10.254.254.0/24*(eth1)
*********|
hub
|
|-*router1*10.254.254.254/24*(eth)*->
->*[*192.168.x.0/24,*10.x.0.0/24,*ecc*]*(isdn)
***********this forwards to a lot of networks through some isdn lines.
|
********|-*router*rete2*10.254.254.252*(eth)->
**** *->*[10.176.x.x]*(isdn)
************this forwards to few 10.176.x.x/255.0.0.0 networks
|
********|-*fw*linux*dmz*10.254.254.251*(eth0)*->
************->*public ip (eth1)*
this is our dmz fw, it forwards to internet*
************ipchains*-A*FORWARD*-s*192.168.0.0/24*-d*0/0*-j*MASQ

this new linuxbox ( i'm thinking debian stable ) should send everithing
according to this routing table ( from the cisco )

firewall>show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS
inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route

Gateway of last resort is 10.254.254.251 to network 0.0.0.0

S 192.10.10.0/24 [1/0] via 10.254.254.254
S 172.16.0.0/16 [1/0] via 10.254.254.254
10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
S 10.100.100.0/24 [1/0] via 10.254.254.254
C 10.254.254.0/24 is directly connected, Ethernet1
S 10.100.1.0/24 [1/0] via 10.254.254.254
S 10.176.0.0/16 [1/0] via 10.254.254.252
C 192.168.0.0/24 is directly connected, Ethernet0
S 194.1.1.0/24 [1/0] via 10.254.254.254
S 200.124.124.0/24 [1/0] via 10.254.254.254
S* 0.0.0.0/0 [1/0] via 10.254.254.251
S 192.168.0.0/16 [1/0] via 10.254.254.254
firewall>quit

the questions are : how do i implement this ? is iptables enough ? do i
need iproute2 or ebtables ? what is the name of the thing i'm going to
build ?
more ... how can the cisco send packets to 192.168.x.x through a
10.254.254.0/24 net without masquerading ? the eth0
( 10.254.254.251/24 ) of the dmz fw receives 192.168.0.x packets
( *ipchains*-A*FORWARD*-s*192.168.0.0/24*-d*0/0*-j*MASQ ) from the eth1
of the cisco ( 10.254.254.253/24 ). what i didn't understand ?
TIA
ivan


ivan