Two NICs, different IPs, same ISP

We have a DELL PowerEdge with two NICs.

eth0 xx.xx.166.46 is an IP part of a class routed trough xx.xx.74.33 (a ZyXEL router).
eth1 xx.xx.74.34 is directly connected to the ISP.

Code:

auto eth0
iface eth0 inet static
        address xx.xx.166.46
        netmask 255.255.255.248
        network xx.xx.166.40
        broadcast xx.xx.166.47
        gateway xx.xx.166.42

auto eth1
iface eth1 inet static
       address xx.xx.74.34
       netmask 255.255.255.0
       network xx.xx.74.0
       broadcast xx.xx.74.255
       gateway xx.xx.74.1

We can not up both interfaces because for some reason they can't work together.

I'm sure this is yet another routing problem but help would be very appreciated.

 

Are these private or a public IPs? Do you get any error messages when you restart the network?

 

Both xx.xx.166.46 and xx.xx.74.34 are public.
xx.xx.166.46's gateway xx.xx.166.42 is routed by xx.xx.74.33.

 

Do you get any error messages when you restart the network?

 

None at all.

Fact is you can not have two default gw as the above setup configures the server.

My question is, what routing options do I have?
If I route default (0.0.0.0) trafic for one gw, how can I also use the other gw?