Problems configuring a bridge type ADSL link.

I need some help here. I seem to have gotten myself in way over my
head with an ADSL install using a SpeedTouch modem.

I've done it a few times with a 'dumb' DLink modem and its been a
breeze. SuSE found the modem, configured it and that was that.

I thought it would be the same with this one, but I was wrong.

I've tried SuSE 8.2, Mandrake 9.1, 9.2 and 10 Beta but still can't
make the thing work.

Now, the details (and this is a bit long winded sorry).

The modem is a Speed Touch 510, has a heap of onboard stuff that is
turned off and its basically just configured as a bridge.

The PC has 2 NICS that have been given static IP's as follows,

eth0 (connected to the modem) 150.101.124.xxx, net mask
255.255.255.252
eth1 (connected to lan) 172.21.103.yyy, net mask 255.255.255.0
The gateway has been given as 150.101.214.xxz

When I configure the nics as above, I can't connect to the modem's web
page because the lan is on a different subnet to the modem (I think)
but I can get to it from a different pc on the lan (this worries me a
bit).

I can ping both the nics, I can ping other lan machines, I can ping
the DNS mach ines (by IP only).

When I try and ping an external machine by IP I get network
unreachable, and by name it just hangs.

I've enabled IP forwarding and, atleast with SuSE, I set the firewall
to be what I've used before successfully (firewall with Mandrake is
very odd to me).

Now, I have no idea where to go from here. I've spent all day on this
and have got absolutely nowhere.

At one stage I had web working with the 9.1 install using squid, but
nothing else was working if thats any use (but I doubt it).

The modem is working OK as I can get to the net from a win box when
its configured to use the modem as a gateway.

I know there is probably a heap of information I haven't given yet,
but thats all I can think of that might be useful at the moment.

Thanks heaps...

Peter Nunn