RH 6.0: Stumped by network: works on L4 IPs, but not L3 IPs

1. Two IPs - one network card - routing not working why???

I am trying to set up my Linux machine (Mandrake 6.1) as a firewall.
Before I do this I want to check I can set multiple IP addresses on our
web side network card and ping it from beyond our router. I have one
network card on a web side network and another on our internal network.
I have a few machines on the web side network (all NT except this Linux
box). When I ping both of the Linux IP addresses on the web side
network from a machine on the same network everything works. When I
ping from a machine on the Internet I only get a reply from one of the
IP addresses. I know my router is configured correctly as the Linux
machine is replacing an NT box. I have tried traceroute but it does not
really tell me anything. I have put enable routing on and off to no
effect. Can anyone help ? I may have no choice but to go back to NT if
I can't fix this !!!

I have included my routing table and details of my ifconfig to see if
someone can spot what I am doing wrong. have I made an obvious mistake
anywhere or is this a bug.

Destination      Gateway      Genmask        Iface
AA.AA.AAA.200    *   eth0
XX.X.XXX.236    XX.X.XXX.233 eth1
XX.X.XXX.234    XX.X.XXX.233 eth1
XX.X.XXX.232    *    eth1
AA.AA.AAA.0      *      eth0        *   L0
default          XX.X.XXX.233          eth1

ifconfig shows
eth0    inet addr : AA.AA.AAA.200 broadcast netmask
eth1    inet addr : XX.X.XXX.236 broadcast XX.X.XXX.239 netmask
eth1:1 inet addr : XX.X.XXX.234 broadcast XX.X.XXX.239 netmask

eth0 is on an internal network and eth1 is on a web side DMZ. Addresses
starting AA.AA.AAA are internal and addresses starting XX.X.XXX are web

When I ping .236 or .234 from web side network everything works fine.
When I ping .236 from beyond our router (.233) I get a reply.
When I ping .234 from beyond the router (.236) I get get 'request timed

Why ???


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