[expert] Two default routes?

[dave]

I am using a Helius satellite router to provide service to a local LAN.
Upstream, DNS and hosting use a 56k leased line. The satellite
router provides a natural firewall, can't be used for incoming
traffic and can't resolve DNS.
Is it possible to use a _single box with two interfaces_ to do this?

Current setup, using two boxes:     
local clients <-> proxy       <-> helius router <-> satellite
a.b.c.0           a.b.c.6           a.b.c.10         0.0.0.0

              <-> Web/DNS  <-> 56k router <-> incoming web traffic
                  a.b.c.5       a.b.c.1         0.0.0.0

Can this be done - one box with two interfaces:

local clients <-> proxy      <-> helius router <-> satellite
a.b.c.0           a.b.c.6         a.b.c.10          0.0.0.0
                  (eth0)

              <-> Web/DNS  <-> 56k router <-> incoming web traffic
                  a.b.c.5       a.b.c.1         0.0.0.0
                  (eth1)
If so, what would the /etc/sysconfig/static-routes look like?

Thanks.