A couple of more things. The command netstat -nr will show you the routing table, so you can check quickly to see if it sees your gateway.
And I believe that using the route command will add the gateway to the /etc/networks file, but if not you could edit it by hand to look something like this:
localnet gateway ip address
And as long as DNS ip addresses in resolv.conf point to vaild DNS servers, then once the route is established it should be able to resolve nemonic names with out a problem.
EDIT: After checking on my laptop, I found a couple of more things. In the /etc/networks file the it won't be the gateway ip address but the network number, which is the subnet that the network is on, ie. 10.10.160.0, or 192.168.0.0. That will tell you box what network is sits on.
And then is the actual command to add the gateway to route.
/sbin/route add default gw (gw ip address) You can also add a line in the /etc/hosts file so you don't have to type the ip address.
The should be a network init script that will start all of this stuff on boot, you my might want to check on that.