Well its pretty similar to doing it on Linux, which is probably no suprise..
to add an IP address to an existing adapter, drop to a shell, and either sudo, or su to root and do
ifconfig en1 inet 192.168.64.25 netmask 255.255.255.0 alias
to add a route do
route add -net 192.168.3.0/24 192.168.0.180
where the first address is the dest route / mask and the 2nd is the gateway...