To add a route for a host (say 192.168.42.10) vi gateway (say 10.1.1.1);
route add host 192.168.42.10 10.1.1.1 1
To add a route for a network (say 192.168.42/24) vi gateway (say 10.1.1.1);
route add net 192.168.42/24 10.1.1.1 1
To add a route for host (say 192.168.42.10) vi direct interface with i.p. 192.168.42.11
route add host 192.168.42.10 192.168.42.11 0
Make sure you also add the entry to /etc/rc so it survives a reboot
Sam