firewall for 2 adsl

[milo974]

hello, actually, we have a firewall with 2 network cards :
Static IP(NET)------Firewall---------lan (switch)
and an other modem router linksys (static ip NET) directly connected on the switch.

192.168.1.250 modem router (cisco) (adsl number 1)
192.168.1.73 (ip address for network card 1firewall)
192.168.0.73 (ip address for network card 2firewall)
192.168.0.0/24 (lan)
192.168.0.1 modem router linksys (adsl number 2)

we have servers that use adsl 1 and other that use adsl 2.
Our firewall is an Openbsd 4.3-release

is it possible to add a third network card and put on it the second modem router ? how to configure pf and nat ?
or pehaps, the easiest way is to put an other firewall to protect the second adsl line ?
What do you advise me?
thank's!