You set your gateway in /etc/defaultrouter. Edit that file with the new IP you need.

To set the IP of the machine you change the entry in /etc/hosts for the hostname of the machine. Make sure /etc/hostname.hme0 (or whichever interface you are using) has the correct hostname in it.

Change both of those and reboot and you'll be all set. If you want to do it without rebooting, make those changes so it does come up correctly next time then do the following:

1. Use the route command to set your default route on the fly. It should be

route add default IP_OF_GATEWAY

but check man route to be sure you get the syntax right for what you're needing to do.

2. Use ifconfig to change the IP address of the interface on the fly. It should be

ifconfig hme0 down
ifconfig hme0 NEW_IP_ADDR
ifconfig hme0 up

Again, use the correct interface if you're not on hme0.

Good luck!

Ralph